Exposure method, illuminating device, and exposure system

ABSTRACT

An exposure method is provided, in which a speckle pattern (interference fringe) formed on a pattern of a transfer objective can be reduced without complicating an illumination optical system so much, without increasing the size of the illumination optical system so much, and without prolonging the exposure time, even when an exposure light beam having high coherence is used. A laser beam (LB) as an exposure light beam from an exposure light source ( 9 ) is introduced into a ring-shaped delay optical system ( 22 ), for example, via a modified illumination mechanism ( 19 ) and a light-collecting lens ( 21 ). A plurality of light fluxes, which have passed through the interior of the delay optical system ( 22 ) a variety of numbers of times depending on angular apertures in accordance with internal reflection, are superimposed and extracted as a laser beam (LB 3 ). The laser beam (LB 3 ) illuminates a reticle (R), for example, via a fly&#39;s eye lens ( 25 ) and a condenser lens ( 7 ).

TECHNICAL FIELD

The present invention relates to an exposure method to be used when amask pattern is transferred onto a substrate such as a wafer in alithography step for producing a device which includes, for example, asemiconductor element, a liquid crystal display element, a plasmadisplay, and a thin film magnetic head. In particular, the presentinvention is suitable for an exposure apparatus based on the use of anilluminating apparatus which is provided with an optical system forrealizing a uniform illuminance distribution on an illuminationobjective.

BACKGROUND ART

A variety of exposure apparatuses are known, including, for example,projection exposure apparatuses of the full-field exposure type or thescanning exposure type (for example, based on the step-and-scan system),and exposure apparatuses based on the proximity system to be used, forexample, when semiconductor elements are produced. Such an exposureapparatus is provided with an illumination optical system forilluminating a pattern on a reticle with a uniform illuminancedistribution by using an illumination light beam (exposure light beam)for exposure in order that the minute pattern on the reticle as a maskis highly accurately transferred onto a wafer (or a glass plate or thelike) applied with resist, as a substrate.

An optical integrator such as a fly's eye lens has been hitherto used asan optical member for uniformizing the illuminance distribution. Anillumination optical system, which is provided with two-stage fly's eyelenses (double fly's eyes) in order to enhance the uniformity of theilluminance distribution, is disclosed, for example, in Japanese PatentApplication Laid-Open No. 6-196389 and U.S. Pat. No. 5,636,003corresponding thereto.

FIG. 17(a) shows main components of a conventional illumination opticalsystem provided with two-stage fly's eye lenses. With reference to FIG.17(a), an illumination light beam IL having a width BW1, which isradiated from an unillustrated exposure light source, comes into a firstfly's eye lens 65. Illumination light beams, which come from a pluralityof light source images formed on a light-outgoing plane of the firstfly's eye lens 65, come into a second fly's eye lens 67 via alight-collecting lens system 66. An illumination light beam, which comesfrom the second fly's eye lens 67, illuminates a reticle R via acondenser lens system 68.

On the other hand, FIG. 17(b) shows main components of a conventionalillumination optical system which has a one-stage fly's eye lens (singlefly's eye). With reference to FIG. 17(b), an illumination light beam IL,which has a width BW2, comes into a fly's eye lens 69. Illuminationlight beams, which come from respective light source images formed onlight-outgoing planes of respective lens elements of the fly's eye lens69, illuminate a reticle R in a superimposed manner via a condenser lenssystem 70.

In the case of the double fly's eye system of the former, the number ofthe light source images formed in a predetermined direction on thelight-outgoing plane of the fly's eye lens 67 is represented by N1·N2provided that N1 and N2 represent the numbers of arrangement of lenselements of the fly's eye lenses 65, 67 in the predetermined direction.On the other hand, in the case of the single fly's eye system of thelatter, it is necessary that the fly's eye lens 69 is subdivided so thatthe number of arrangement of the fly's eye lens 69 is about N1·N2 in apredetermined direction in order to obtain the same degree of theuniformity of the illuminance distribution as that of the double fly'seye system in the predetermined direction.

The exposure light beam has a narrow wavelength width, and it hasrelatively high coherence (coherency). Therefore, if the exposure lightbeam is used as it is, then interference fringes which are calledspeckles are generated on the illumination area of the reticle, and itis feared that any unevenness of the exposure amount is caused thereby.In view of this fact, in order to reduce the temporal coherence of theexposure light beam (or shorten the coherence time) and reduce theinterference fringes, Japanese Patent Publication No. 7-104500 (JapanesePatent No. 2071956) discloses a delay optical system in which theexposure light beam is divided into two by using a beam splitter, andtwo-divided light fluxes are superimposed again after giving apredetermined difference in optical path to them. On the other hand,Japanese Patent No. 2590510 discloses an exposure apparatus in which thetemporal coherence is reduced by radiating an exposure light beam onto abeam splitter surface of a delay optical system having a polygonal crosssection in which one surface is the beam splitter surface and theremaining surfaces are reflecting surfaces (or total reflectionsurfaces).

As described above, the conventional exposure apparatus uses theillumination optical system which is provided with the one-stage opticalintegrator or the two-stage optical integrators. Further, the techniqueto avoid the occurrence of speckles has been developed. In suchcircumstances, the exposure wavelength is shortened in an advancedmanner in recent years in order to obtain a higher resolution. Atpresent, the KrF excimer laser light beam (wavelength: 248 nm) isdominantly used. In future, investigation will be made to use the vacuumultraviolet light beam such as the ArF excimer laser light beam(wavelength: 193 nm) and the F₂ laser light beam (wavelength: 157 nm).Such a laser beam has high coherence as compared with the conventionalbright line. When the laser beam having the short wavelength asdescribed above is allowed to pass through a projection optical systemcomposed of a refractive system, then the usable saltpeter material islimited, for example, to quartz glass and fluorite, and it is difficultto extinguish the color. Therefore, the wavelength of the laser beam isusually narrow-banded, for example, to have an order of the half valuewidth of about 0.1 to 1 pm. The coherence of the laser beamnarrow-banded as described above is further enhanced, resulting in highcontrast of the interference fringes (speckles). Therefore, it isnecessary to use a more highly-advanced technique in order to avoid theoccurrence of interference fringes.

Recently, the areal size per one chip of the semiconductor element isincreased. Further, it is also effective to increase the numericalaperture of the projection optical system in order to obtain a higherresolution. However, it gradually becomes difficult to design andproduce a projection optical system with which high image formationperformance is successfully obtained over an entire exposure area thatis large and wide. In view of the above, the attention is attracted to ascanning exposure type projection exposure apparatus in which exposureis performed by synchronously moving a reticle and a wafer with respectto a projection optical system in a state in which an exposure lightbeam is radiated into a slender slit-shaped illumination area on thereticle. In this case, the narrower the width of the illumination areain the scanning direction (hereinafter referred to as “slit width”) is,the wider the width of the exposure field is, when a projection opticalsystem having an identical size is used. As a result, it is possible toperform the exposure for a chip pattern having a large areal size.However, when the pulse light beam such as the excimer laser light beamis used, it is necessary that the number of exposure pulses for eachpoint on the wafer is not less than a predetermined minimum number ofpulses, taking the dispersion or irregularity of the pulse energy intoconsideration. When the movement velocity of the stage is increased inorder to enhance the throughput in a state in which the slit width ismade narrow, the number of exposure pulses is consequently decreased.However, it is possible to increase the frequency of the pulse lightemission in the case of the recent excimer laser light source. Theproblem of the number of exposure pulses has been progressivelydissolved.

However, when the slit width is narrowed, if a fly's eye lens is used asthe optical integrator, then it is necessary to use finely subdividedlens elements in the scanning direction to such an extent correspondingto the narrowed slit width. When the arrangement pitch of a plurality oflens elements is made fine as described above, the interference fringestend to occur in the illumination area of the reticle, because thecoherence of the light fluxes passing through the adjacent lens elementsis enhanced.

That is, in the case of the double fly's eye system shown in FIG. 17(a),the width of each lens element of the fly's eye lens 65 at the firststage can be wider than Δ provided that Δ represents the coherencelength in the lateral direction of the illumination light beam IL. Inthis case, it is assumed that the light fluxes A1, A2, which come intopositions in the vicinity of the interface between certain adjacent lenselements of the fly's eye lens 65, come into the different points P1, P2on the reticle R respectively. It is also assumed that the light fluxesB1, B2, which come into positions separated from the boundary betweenthe lens elements by spacing distances Δ1, Δ2 (assuming that Δ1+Δ2=Δ issatisfied) respectively, also come into the points P1, P2 respectivelyvia the fly's eye lens 67. Interference occurs at the points P1, P2,respectively and interference fringes are formed on the reticle R.

Similarly, in the case of the single fly's eye system shown in FIG.17(b), it is assumed that the light fluxes A3, A4, which come into acertain boundary between the lens elements, come into the differentpoints P3, P4 on the reticle R respectively, and the light fluxes B3,B4, which come into a boundary adjacent thereto, also come into thepoints P3, P4 respectively, provided that the lens element of the fly'seye lens 69 has the width which is formed to be narrow in the samedegree as that of the coherence length Δ in the lateral direction of theillumination light beam IL. Also in this case, interference occurs atthe points P3, P4, respectively and interference fringes are formed onthe reticle R.

That is, it is necessary to use the optical integrator in order torealize the uniform illuminance distribution on the reticle of the laserbeam in which the illuminance distribution has a shape of Gaussiandistribution. However, if the reticle is illuminated in a superimposedmanner by using the optical integrator, the interference fringes tend toappear. An exposure apparatus has been also developed, in which arod-type integrator (rod lens) is used as the optical integrator.However, the conventional rod-type integrator involves such aninconvenience that the interference fringes tend to appear in the samemanner as in the fly's eye lens.

In view of the above, in order to decrease the temporal coherence anddecrease the interference fringes, it is also possible to use the delayoptical system or the delay optical element as described above incombination. However, the conventional delay optical system and thedelay optical element have such a tendency that the size is increasedand the weight is increased, for the recent exposure light beam composedof the laser beam which is narrow-banded and which has the highcoherence. If the delay optical system or the delay optical element isallowed to have a function to uniformize the illuminance distribution aswell, it is possible to simplify the arrangement of the illuminationoptical system.

In order to mitigate the uneven illuminance caused by the interferencefringes without using the delay optical system or the delay opticalelement, for example, the following method has been hitherto used aswell. That is, a vibration mirror is arranged in front of the fly's eyelens, and the laser beam, which comes into the fly's eye lens, isvibrated to move the interference fringes on the reticle. By doing so,the uneven illuminance is reduced by means of the integrating effect. Inthis case, the control is made so that the interference fringes aregradually moved every time when the pulse light emission is performed,because the excimer laser or the like resides in the pulse light beam.However, in the case of the method based on the use of the vibrationmirror as described above, it is necessary to ensure a certain degree ofexposure time. For this reason, an inconvenience arises as follows. Thatis, if it is intended to obtain necessary uniformity of the exposureamount distribution, then the exposure time is prolonged, and thethroughput is lowered.

Taking the foregoing points into consideration, a first object of thepresent invention is to provide an exposure method in which asubstantially uniform illuminance distribution is obtained on a patternof a transfer objective without complicating an illumination opticalsystem so much, without increasing the size of the illumination opticalsystem so much, and without prolonging the illumination time (exposuretime), even when an illumination light beam (exposure beam orillumination beam) having high coherence is used.

A second object of the present invention is to provide an illuminatingapparatus which can be used when the exposure method as described aboveis carried out.

A third object of the present invention is to provide an exposureapparatus which makes it possible to perform exposure with a highthroughput and with small unevenness of exposure amount by using theilluminating apparatus as described above.

A fourth object of the present invention is to provide an exposuremethod which makes it possible to improve uniformity of totalizedexposure amount distribution on an exposure objective substrate afterscanning exposure without increasing the size of an illumination opticalsystem so much, when the scanning exposure is performed by using a pulselight beam (exposure beam or illumination beam) having high coherence.

A fifth object of the present invention is to provide an illuminatingapparatus or an exposure apparatus which can be used when the exposuremethod as described above is carried out.

DISCLOSURE OF THE INVENTION

A first exposure method according to the present invention resides in anexposure method for illuminating a first object (R) with an exposurelight beam to transfer a pattern on the first object onto a secondobject (W), the exposure method comprising adjusting the exposure lightbeam into light fluxes having a predetermined angular aperturedistribution, and allowing the adjusted light fluxes to pass through asubstantially closed loop-shaped optical path so that a plurality oflight fluxes, which have passed through the loop-shaped optical path avariety of numbers of times depending on angular apertures respectively,are superimposed and guided to the first object.

According to the present invention as described above, when the exposurelight beam, which has the predetermined angular aperture or open angledistribution, is supplied to the loop-shaped optical path, thecomponents of the exposure light beam, which have different angularapertures or open angles (angles of incidence), are advanced whilerepeating reflections at the outer circumferential surfaces of theoptical path depending on the angular apertures respectively. In thisoperation, for example, when a window, which is smaller than the crosssection of the optical path, is formed at an intermediate position ofthe optical path beforehand, the components, which pass through thewindow, are radiated toward the first object. On the other hand, thecomponents, which are spread widely beyond the window, pass through theoptical path again, and the components, which pass through the window,are finally radiated toward the first object. As a result, thecomponents, which have passed through the loop-shaped optical path once,twice, three times or more depending on the angular aperturesrespectively, are superimposed and radiated from the window.

When the optical path length, which is required for the light flux topass through the loop-shaped optical path once, is set to be longer thanthe coherence length that is determined depending on the coherence time,the coherence between the plurality of components is greatly loweredowing to the delay effect. That is, the temporal coherence of theexposure light beam radiated from the window is lowered owing to thedelay effect depending on the angular apertures of the respectivecomponents, and the spatial coherence thereof is also lowered. Further,the information on the angular aperture (angle of incidence) upon theincidence is maintained by the reflection at the outer circumference.Further, the illuminance distribution is uniformized as well by therepeated reflection at the outer circumference. In other words, thelight flux is divided (subjected to wave front division) depending onthe size of the cross section of the loop-shaped optical path and thesize of the window for radiation. Therefore, the delay effect and theuniformizing effect of the illuminance distribution are obtained owingto the loop-shaped optical path. Accordingly, even when the exposurelight beam has a Gaussian distribution with high coherence, then theinterference fringes (speckles) on the pattern of the transfer objectiveare reduced on condition that the illumination optical system issimplified, and it is possible to obtain a substantially uniformilluminance distribution.

In another aspect, a first illuminating apparatus of the presentinvention resides in an illuminating apparatus for illuminating apattern on an illumination objective (R) with an illumination light beamfrom a light source (15), the illuminating apparatus comprising anoptical member (22) including a window (44) which receives theillumination light beam from the light source, wherein a plurality oflight fluxes, which are obtained by allowing light fluxes incoming fromthe window to pass through the optical member (22) a variety of numbersof times depending on angular apertures respectively, are superimposedand radiated toward the illumination objective. According to the presentinvention as described above, the optical member (22) forms aloop-shaped optical path to act as a delay optical element for theillumination light beam and an element for uniformizing the illuminancedistribution. Therefore, it is possible to use the first exposure methodaccording to the present invention.

In this arrangement, it is desirable that an angular aperture-adjustingoptical system (21) for adjusting the illumination light beam from thelight source into light fluxes having a predetermined angular aperturedistribution is arranged between the light source and the opticalmember; and a multiple light source-forming optical system (25) forforming a plurality of light source images from the illumination lightbeam from the optical member, and a condenser optical system (7) forradiating light fluxes from the plurality of light source images ontothe illumination objective in a superimposed manner are arranged betweenthe optical member and the illumination objective.

It is desirable that the window (44) is arranged at a position which iseccentric from a central axis of the optical member (22). It ispreferable that the window also serves as a window for radiating theillumination light beam. Examples of the optical member include thoseobtained by arranging, in a ring-shaped configuration, outer surfacereflection members (for example, mirrors) or prism-shaped or columnartransmitting members (for example, rod members).

When the window is eccentric from the central axis of the opticalmember, the incoming illumination light beam arrives at the reflectingsurfaces under different conditions in the upward, downward, rightward,and leftward directions. As a result, the delay condition (for example,the number of times of passage through the loop), which is determineddepending on the angular aperture, is mutually different in the upward,downward, rightward, and leftward directions. The delay condition forthe illumination light beam advancing in an oblique direction is acondition obtained by averaging the delay conditions in the upward anddownward directions and in the rightward and leftward directions in thevicinity thereof. As a result, one optical member can be used as a largenumber of delay optical systems having different delay conditions. Thetemporal coherence is further lowered.

Besides the window is eccentric from the central axis of the opticalmember as described above, it is also preferable that the direction ofthe illumination light beam supplied to the window is allowed to have apredetermined inclination with respect to the central axis.

In still another aspect, a first exposure apparatus according to thepresent invention resides in an exposure apparatus for transferring apattern on a first object onto a second object, wherein the pattern onthe first object is illuminated with an illumination light beam from theilluminating apparatus of the present invention.

In still another aspect, a second exposure apparatus according to thepresent invention resides in an exposure apparatus provided with anillumination system for illuminating a first object (R) with an exposurelight beam in which a second object (W) is exposed with the exposurelight beam via the first object; the exposure apparatus comprising anoptical member (22) which includes a transmitting section (22 a to 22 h)for internally reflecting the exposure light beam in the illuminationsystem and changing a traveling direction thereof; wherein the opticalmember is formed with an aperture (44) which is smaller than across-sectional area of the transmitting section in order to radiate theexposure light beam. When the exposure apparatuses as described aboveare used, then interference fringes are scarcely formed on the firstobject, and the exposure amount distribution is uniformized.Accordingly, it is possible to improve the line width uniformity of thepattern to be transferred onto the second object.

In still another aspect, a second exposure method according to thepresent invention resides in an exposure method for illuminating a firstobject (R) with an exposure light beam to expose a second object (W)with the exposure light beam having passed through a pattern on thefirst object; the exposure method comprising introducing the exposurelight beam into a plane (76G) which is substantially conjugate with apattern plane of the first object via an open light-feeding optical path(56) which is surrounded by reflecting surfaces and which has at leastone bent section (58A), and introducing, into the first object, theexposure light beam having passed through the plane.

According to the present invention as described above, a plurality oflight source images (secondary light sources) are formed as virtualimages in accordance with the reflection at external surfaces of thelight-feeding optical path in the same manner as in a rod-typeintegrator. In this procedure, the coherence is lowered for the adjacentlight source images, because they are inverted in relation to thereflecting surfaces. As a result, the contrast is lowered forinterference fringes (speckles) generated on the first object. Theformation of the plurality of light source images can be considered aswave front division of the exposure light beam as well. When the angularaperture of the exposure light beam (coherence factor of theillumination system) is increased, or when the light-feeding opticalpath is lengthened, then the number of formed light source images(number of wave front division) is increased, the integration effect isenhanced, and the coherence is decreased as well. Therefore, it ispossible to improve the uniformity of the illuminance distribution onthe pattern of the first object. However, when the light-feeding opticalpath is merely lengthened, the illumination optical system inevitablyhas a large size. However, in the present invention, the light-feedingoptical path is bent. Therefore, the illumination optical system can beminiaturized.

In this arrangement, for example, when a laser beam, in which theoscillation wavelength width is narrow-banded to have an order of about0.1 to 1 pm, is used, it is desirable that the light-feeding opticalpath is provided with at least three bent sections, in order that thelight-feeding optical path is sufficiently long to obtain a sufficientlyuniform illuminance distribution on the pattern of the first object, andthe illumination optical system is allowed to have a small size.

It is desirable that a width of the light-feeding optical path (56) on alight-outgoing side (57B) is wider than a width of the light-feedingoptical path (56) on a light-incoming side (57A) in a bending directionbrought about by the bent section (58A). One method for increasing thenumber of wave front division as described above is to increase theangular aperture of the exposure light beam. However, if the angularaperture is increased in a state in which the cross-sectional area ofthe light-feeding optical path is constant, the light amount loss isincreased at the bent section. On the contrary, when the width d2 on thelight-outgoing side is made wider than the width d1 on thelight-incoming side of the light-feeding optical path, it is possible todecrease the light amount loss at the bent section.

In still another aspect, a third exposure method according to thepresent invention resides in an exposure method for illuminating a firstobject (R) with a pulse-emitted exposure light beam and synchronouslymoving the first object and a second object (W) to perform scanningexposure for the second object with the exposure light beam havingpassed through a pattern on the first object; the exposure methodcomprising previously measuring a repeating pitch (Q1) of an intensitydistribution of the exposure light beam on the second object in ascanning direction for the second object; and setting a distance (Q2) ofmovement of the second object in the scanning direction during one cycleof pulse light emission of the exposure light beam to be a non-integralmultiple of the measured pitch.

In the present invention as described above, even if any unevenness(interference fringe or the like) of the intensity distribution havingthe pitch Q1 is generated on the second object in the scanning directionfor the second object by the exposure light beam in an amount of onepulse, the exposure light beam is subjected to the pulse light emissionevery time when the second object is moved in the scanning direction bythe distance Q2 (≠n·Q1, n is an integer of not less than 1).Accordingly, the distribution of the totalized exposure amount on thesecond object is gradually uniformized owing to the averaging effect.

In still another aspect, a second illuminating apparatus according tothe present invention resides in an illuminating apparatus forilluminating a pattern on an illumination objective (R) with anillumination light beam from a light source (9); the illuminatingapparatus comprising a multiple light source-forming optical system (56)which includes a plurality of transmitting sections (57A to 57G)surrounded by reflecting surfaces respectively for allowing theillumination light beam to pass through an interior thereof, and one ora plurality of reflecting section or sections (58A to 58F) for bendingan optical path for the illumination light beam at a boundary betweenthe plurality of transmitting sections, in which the illumination lightbeam is incorporated at one transmitting section (57A) of the pluralityof transmitting sections, and the illumination light beam is radiatedfrom another transmitting section (57G) onto a plane (76G) that issubstantially conjugate with a pattern plane of the first object; and acondenser optical system (31, 7) which collects, onto the pattern, theillumination light beam having passed through the substantiallyconjugate plane.

In still another aspect, a third exposure apparatus according to thepresent invention resides in an exposure apparatus comprising the secondilluminating apparatus of the present invention which illuminates afirst object (R) as an illumination objective with an illumination lightbeam from the illuminating apparatus; wherein a second object (W) isexposed with the illumination light beam having passed through a patternon the first object.

In still another aspect, a fourth exposure apparatus according to thepresent invention resides in an exposure apparatus having anillumination system for illuminating a first object (R) with an exposurelight beam, for exposing a second object (W) with the exposure lightbeam via the first object; the exposure apparatus comprising an opticalmember (56) which includes a transmitting section (57A, 58A, 57B) forinternally reflecting the exposure light beam in the illuminationsystem; wherein the transmitting section of the optical member is bentat least at one position, and a width (width d2) of the transmittingsection after being bent is larger than a width (width d1) of thetransmitting section before being bent.

In still another aspect, a fifth exposure apparatus according to thepresent invention resides in an exposure apparatus for illuminating afirst object with an exposure light beam from a pulse light source (9)and synchronously moving the first object and a second object by the aidof a stage system (1, 4, 5) to perform scanning exposure for the secondobject with the exposure light beam having passed through a pattern onthe first object; the exposure apparatus comprising a storage unit (13a) which stores a repeating pitch of an intensity distribution of theexposure light beam on the second object in a scanning direction for thesecond object; and a control system (13) which controls a light emissionfrequency of the pulse light source and a scanning velocity of thesecond object effected by the stage system depending on the storedpitch.

The second exposure method and the third exposure method can be carriedout by using the second illuminating apparatus and the third and fourthexposure apparatuses and the fifth exposure apparatus of the presentinvention respectively.

It is desirable for the fifth exposure apparatus to provide aphotoelectric detector (2) for measuring the intensity distribution onthe stage for driving the second object.

In still another aspect, a method for producing a device according tothe present invention comprises the step of transferring a devicepattern (R) onto a workpiece (W) by using the exposure method of thepresent invention as described above. When the present invention isapplied, the unevenness of the exposure amount is reduced. Therefore, itis possible to produce a device having a highly advanced function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic arrangement illustrating a projection exposureapparatus according to a first embodiment of the present invention.

FIG. 2 shows an arrangement illustrating an illumination system 8 shownin FIG. 1.

FIG. 3 illustrates an arrangement and function of a modifiedillumination mechanism 19 shown in FIG. 2.

FIG. 4 illustrates a case in which the modified illumination mechanism19 shown in FIG. 3 is used to perform annular illumination.

FIG. 5 shows another illustrative arrangement of the modifiedillumination mechanism.

FIG. 6 illustrates an arrangement and function of a delay optical system22 shown in FIG. 2.

FIG. 7 shows a plurality of light fluxes which pass through the delayoptical system 22 shown in FIG. 6 a variety of numbers of timesdepending on angular apertures.

FIG. 8(a) shows a perspective view illustrating the delay optical system22 shown in FIG. 2, FIG. 8(b) shows a perspective view illustrating anaperture 44 disposed at a light-incoming/outgoing plane 43 of the delayoptical system 22 shown in FIG. 2, FIG. 8(c) shows a perspective viewillustrating a first modified embodiment of a window provided on thelight-incoming/outgoing plane 43, and FIG. 8(d) shows a perspective viewillustrating a second modified embodiment of the window provided on thelight-incoming/outgoing plane 43.

FIG. 9 shows a variety of modified embodiments of the delay opticalsystem 22 shown in FIG. 2.

FIG. 10 shows a schematic arrangement illustrating a projection exposureapparatus according to a second embodiment of the present invention.

FIG. 11 shows, with partial cutaway, an arrangement illustrating, forexample, an illumination system 8 shown in FIG. 10.

FIG. 12 illustrates an arrangement and function of a bent typerod-shaped optical member 56 shown in FIG. 11.

FIG. 13 illustrates an effect obtained by gradually widening the widthsin the bending direction of two adjacent rod members of the bent typerod-shaped optical member 56 shown in FIG. 11.

FIG. 14 shows another illustrative arrangement of the bent typerod-shaped optical member 56.

FIG. 15 illustrates the relationship between the pitch Q1 of theilluminance distribution in an exposure area on a wafer and the distanceof movement of the wafer obtained every time when an exposure light beamis subjected to pulse light emission.

FIG. 16 illustrates the operation effected to measure the pitch Q1 ofthe illuminance distribution of the exposure area by using an unevenilluminance sensor 2.

FIG. 17(a) shows a conventional illumination system based on the doublefly's eye system, and FIG. 17(b) shows a conventional illuminationsystem based on the single fly's eye system.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred first embodiment of the present invention will be explainedbelow with reference to FIGS. 1 to 9. In this embodiment, the presentinvention is applied when exposure is performed with a projectionexposure apparatus based on the step-and-scan system.

FIG. 1 shows a schematic arrangement of the projection exposureapparatus of this embodiment. With reference to FIG. 1, a laser beam LB,which has a narrow-banded wavelength as an illumination light beam forexposure (exposure light beam) pulse-emitted from an exposure lightsource 9, comes into an illumination system 8. A KrF excimer laser lightsource (oscillation frequency: 248 nm), in which the oscillationwavelength width is narrow-banded, for example, into about 0.1 to 1 pm,is used as the exposure light source 9 in this embodiment. However,other than the above, the present invention is also applicable to a caseto use an exposure light source for generating, for example, a laserbeam having high coherence such as ArF excimer laser (wavelength: 193nm) and F₂ laser (wavelength: 157 nm) as well as a high harmonic wavegenerator for YAG laser. Further, for example, an X-ray source can bealso used for the exposure light source 9. The light sources asdescribed above are pulse light sources. However, the present inventionis also applicable to a case to use a light source which continuouslyemits light.

The illumination system 8 is provided with an optical system forconverting the cross-sectional configuration of the incoming light fluxinto a desired shape as described later on, an optical member forreducing the temporal coherence, a fly's eye lens to serves as anoptical integrator (uniformizer or homogenizer), and a field diaphragm(reticle blind). The incoming laser beam LB is converted by theillumination system 8 into an illumination light beam IU which has apredetermined numerical aperture and which has a uniformized illuminancedistribution. The illumination light beam IU passes through a condenserlens system 7, and a pattern plane of a reticle R is illuminated with aslender illumination area having a rectangular configuration. Under theillumination light beam IU, an image of a pattern on the reticle R as afirst object or a mask is projected via a projection optical system 3 ata projection magnification β (β is, for example, ¼, ⅕, or ⅙) onto arectangular exposure area on a wafer W applied with resist as a secondobject or a substrate. The wafer W is, for example, a disk-shapedsubstrate for producing a semiconductor device such as semiconductor(silicon or the like) or SOI (silicon on insulator). Explanation will bemade below assuming that the X axis extends in parallel to the plane ofpaper of FIG. 1 in the plane perpendicular to the optical axis AX of theprojection optical system 3, and the Y axis extends perpendicularly tothe plane of paper of FIG. 1. The scanning direction during the scanningexposure for the reticle R and the wafer W in this embodiment is the Ydirection.

In this arrangement, the reticle R is held on a reticle stage 5. Thereticle stage 5 is continuously movable in the Y direction on a reticlebase 4, for example, in accordance with the linear motor system, and itis finely movable to correct, for example, any synchronization error inthe X direction, the Y direction, and the rotational direction. The Xcoordinate, the Y coordinate, and the angle of rotation of the reticlestage 5 are measured highly accurately by means of laser interferometersprovided for a reticle stage control system 12. The reticle stagecontrol system 12 drives the reticle stage 5 on the basis of an obtainedresult of the measurement and control information supplied from a maincontrol system 13.

On the other hand, the wafer W is held on a wafer stage 1 by the aid ofan unillustrated wafer holder. The wafer stage 1 is continuously movablein the Y direction on an unillustrated surface plate, for example, inaccordance with the linear motor system, and it is movable in a steppingmanner in the X direction and the Y direction. The wafer stage 1controls the focus position (position in the Z direction) and the angleof inclination of the wafer W in accordance with the servo system on thebasis of a result of detection obtained by an unillustrated autofocussensor so that the surface of the exposure area of the wafer W coincideswith the image plane of the projection optical system 3. The Xcoordinate, the Y coordinate, and the angle of rotation of the waferstage 1 are measured highly accurately by means of laser interferometersprovided for a wafer stage control system 11. The wafer stage controlsystem 11 drives the wafer stage 1 on the basis of an obtained result ofthe measurement and control information supplied from the main controlsystem 13. An illumination control system 10 is connected to the maincontrol system 13. The illumination control system 10 controls, forexample, the light emission timing and the light emission output of theexposure light source 9, and it controls the operation of predeterminedmembers in the illumination system 8 (as described in detail later on).Accordingly, the illumination control system 10 sets the illuminationcondition (for example, switching between the ordinary illumination andthe modified illumination and setting of the σ value as the coherencefactor of the illumination light beam).

During the scanning exposure, the illumination condition is set by theillumination control system 10 under the control of the main controlsystem 13. After the pulse light emission is started by the exposurelight source 9, the reticle R is moved at a velocity VR in the +Ydirection (or in the −Y direction) by the aid of the reticle stage 5, insynchronization with which the wafer W is moved at a velocity β·VR (βrepresents the projection magnification from the reticle R to the waferW) in the −Y direction (or in the +Y direction) by the aid of the waferstage 1. Accordingly, one shot area on the wafer W is exposed with thelight beam. The reason whey the scanning direction of the reticle R isopposite to that of the wafer W is that the projection optical system 3performs the inversion projection. After that, the operation, in whichthe wafer W is moved in a stepping manner so that the next shot areacomes to a position just before the exposure area to perform thesynchronized scanning, is repeated in accordance with the step-and-scansystem. Thus, the respective shot areas on the wafer W are exposed withthe pattern image of the reticle R.

Next, explanation will be made in detail for the arrangement of theexposure light source 9 and the illumination system 8 of thisembodiment.

FIG. 2 shows the arrangement of the exposure light source 9 and theillumination system 8 shown in FIG. 1. With reference to FIG. 2, theexposure light source 9 comprises a main laser light source body 15 forgenerating the linearly polarized laser beam LB, a beam-matching unit(BMU) 16 for transmitting the laser beam LB to the illumination system8, and a laser power source unit 17 for driving the main laser lightsource body 15. The laser power source unit 17 effects, for example, thecontrol of the pulse light emission timing of the laser beam LB at themain laser light source body 15, the fine adjustment for the oscillationfrequency, and the fine adjustment for the light emission power (averagepulse energy) under the control of the illumination control system 10.

In the illumination system 8, the laser beam LB is dimmed to have apredetermined illuminance (=average pulse energy per unit area xoscillation frequency) by the aid of a dimming unit 18. When the pulseemission type laser beam LB (illumination light beam IU) is used as theexposure light beam or the illumination light beam as in thisembodiment, it is necessary that the number of exposure pulses N (N isan integer) for each point on the wafer is not less than a predeterminedminimum number of pulses N_(min) which is determined depending on thedispersion of the pulse energy, in order to allow the totalized exposureamount at each point on the wafer to be included within an allowablerange with respect to a proper value. Further, assuming that E [J/mm²]represents the resist sensitivity (proper exposure amount) on the waferW and P [J/mm²] represents the average pulse energy on the wafer W, itis necessary that the following relationship holds within apredetermined allowable range by using the number of exposure pulses N.

E=N·P  (1)

Assuming that V [mm/s] represents the scanning velocity of the waferstage 1, D represents the width in the scanning direction (Y direction)of the slit-shaped exposure area on the wafer W (slit width on thewafer), and f[/s] represents the oscillation frequency of the laser beamLB, the number of exposure pulses N is represented by the followingexpression.

N=f·(D/V)≧N _(min)  (2)

The following expression is obtained by substituting the expression (1)with the expression (2).

E·V=f·P·D  (3)

Accordingly, assuming that the slit width D is fixed, the main controlsystem 13 firstly determines the values of the oscillation frequency fand the scanning velocity V so that f·(D/V)≧N_(min) in the expression(2) holds. In response thereto, the illumination control system 10 setsthe oscillation frequency f of the laser beam LB for the laser powersource unit 17. Subsequently, the main control system 13 calculates thevalue of the average pulse energy P by substituting the expression (1)with the number of exposure pulses N and the resist sensitivity E. Aresult of the calculation is supplied as a target value to theillumination control system 10. In this procedure, the proportionalconstant is previously determined between the illuminance of the laserbeam LB on the light-incoming plane of the dimming unit 18 and theilluminance of the illumination light beam IU on the wafer W for a casein which a standard aperture diaphragm is used for the illuminationoptical system. The proportional constant is stored in a storage unit inthe illumination control system 10. The illumination control system 10sets the dimming ratio (transmittance) for the dimming unit 18 so thatthe pulse energy P of the illumination light beam IU on the wafer is thetarget value described above, from the proportional constant, thepresent state of the aperture diaphragm, and the pulse energy of thelaser beam LB. The final adjustment is performed highly accurately onthe basis of an unillustrated integrator sensor.

The laser beam LB, which has passed through the dimming unit 18, isshaped by a modified illumination mechanism 19 so that the illuminancedistribution in cross section is in a predetermined state (for example,circular, annular, and eccentric plural light sources) and theilluminance distribution is a substantially uniform distribution. Alaser beam LB2, which has been shaped as described above, is oncecollected by a light-collecting lens 21, and then it behaves as lightfluxes having predetermined angular apertures to come into an aperture44 on a light-incoming/outgoing plane 43 of a delay optical system 22which is composed of a quadrilateral frame-shaped transmitting member.The delay optical system 22 is formed by joining, into a quadrilateralframe-shaped configuration, four rectangular prisms 22 a, 22 c, 22 e, 22g and four quadratic prism-shaped rod members 22 b, 22 d, 22 f, 22 hwhich are transmissive with respect to the laser beam LB respectively.Further, the outer circumferential surfaces of the delay optical system22 are reflecting surfaces except for the aperture on thelight-incoming/outgoing plane 43 (as described in detail later on).

The delay optical system 22 corresponds to the optical member of thepresent invention, the optical path in the delay optical system 22corresponds to the substantially closed loop-shaped optical path of thepresent invention, and the aperture 44 corresponds to the window. Thelight fluxes, which have passed through the delay optical system 22once, twice, three times . . . , are superimposed to be radiated as alaser beam LB3 from the aperture on the light-incoming/outgoing plane 43in a direction substantially perpendicular to the incoming direction ofthe laser beam LB2. The areal size of the projection, which is obtainedby projecting the aperture 44 onto the plane perpendicular to thecentral axis of the delay optical system 22, is set, for example, to beabout 1/(10×10) with respect to the cross-sectional area of, forexample, the quadratic prism-shaped rod member 22 b of the delay opticalsystem 22. Accordingly, the illuminance distribution is uniformizedequivalently to a case in which light fluxes, which are obtained bydividing (effecting the wave front division for) the incoming laser beamLB2 into about 100 individuals, are superimposed again. Further, thetemporal coherence is greatly lowered in the outgoing laser beam LB3 ascompared with the incoming laser beam LB2.

The laser beam LB3, which is radiated from the delay optical system 22,is deflected by a wedge-shaped aberration-correcting prism 23 so thatthe laser beam LB3 travels along the optical axis of the illuminationoptical system. After that, the laser beam LB3 comes into a fly's eyelens 25 as an optical integrator (homogenizer) via a lens 24. The fly'seye lens 25 corresponds to the multiple light source-forming opticalsystem of the present invention. Assuming that the fly's eye lens 25 isformed by bundling, for example, lens elements of about 10 rows×10columns, the laser beam LB3 is divided (subjected to wave frontdivision) into about 100 individuals by the fly's eye lens 25. Dividedlight fluxes are radiated as the illumination light beam IU in asuperimposed manner. That is, the wave front division, whichsubstantially corresponds to about 100×100 individuals, is performed bythe delay optical system 22 and the fly's eye lens 25. Therefore, theilluminance distribution of the illumination light beam IU radiated fromthe fly's eye lens 25 is sufficiently uniformized.

A diaphragm-switching member 27, which is formed with a variety ofaperture diaphragms for finally determining the illumination condition(for example, ordinary illumination, modified illumination, andillumination with small coherence factor (small σ value)) and the σvalue, is rotatably arranged in the vicinity of the light-outgoing planeof the fly's eye lens 25, i.e., at the optical Fourier transformationplane (pupil plane) with respect to the pattern plane of the reticle Ras the focus plane on the light-outgoing side of the fly's eye lens 25or in the vicinity thereof. The illumination control system 10 rotatesthe diaphragm-switching member 27 by the aid of a driving motor 26 toarrange a predetermined aperture diaphragm at the light-outgoing planeof the fly's eye lens 25. Thus, the illumination condition and the avalue are set. The illumination light beam IU, which outgoes from thefly's eye lens 25 and which passes through the predetermined aperturediaphragm, passes through a relay lens 28, a movable blind 29B, a fixedblind 29A, and a relay lens 31, and it is radiated from the illuminationsystem 8. After that, the illumination area on the reticle R isuniformly illuminated with the illumination light beam IU via acondenser lens 7.

In this arrangement, the fixed blind 29A is arranged in the vicinity ofthe conjugate plane with respect to the pattern plane of the reticle R.The slit-shaped illumination area on the reticle R is defined by anaperture of the fixed blind 29A. The movable blind 29B is arrangedclosely to the fixed blind 29A. The movable blind 29B plays a role toshield the aperture of the fixed blind 29A in order that any unnecessarypattern is transferred onto the wafer upon the start and the end of thescanning exposure for each of the shot areas on the wafer. Theillumination control system 10 controls the operation of the movableblind 29B by the aid of a driving unit 30 in accordance with thesynchronization information supplied from the main control system 13.

Although not shown, for example, a beam splitter is arranged between thediaphragm-switching member 27 and the relay lens 28. An integratorsensor is provided, which photoelectrically converts the illuminationlight beam incorporated by the aid of the beam splitter. A detectionsignal obtained by the integrator sensor is supplied to the illuminationcontrol system 10. The relationship between the detection signal of theintegrator sensor and the illuminance of the illumination light beam IUon the wafer W is previously measured, and it is stored in the storageunit in the illumination control system 10. The illumination controlsystem 10 controls, for example, the laser power source 17 and thedimming unit 18 so that the illuminance of the illumination light beamIU on the wafer W has a target value set by the main control system 13.

Next, an illustrative arrangement of the modified illumination mechanism19 of this embodiment will be explained in detail with reference toFIGS. 3 and 4. FIG. 3(a) shows the modified illumination mechanism 19included in the illumination system 8 shown in FIG. 2. With reference toFIG. 3(a), the laser beam LB, which is supplied in the linearlypolarized state from the exposure light source 9 shown in FIG. 2 andwhich has passed through the dimming unit 18, is converted by a ¼wavelength plate 32 into a circularly polarized light beam that comesinto a polarizing beam splitter 33. A P-polarized first light flux ofthe incoming laser beam LB, which has transmitted through the polarizingbeam splitter 33, passes along a mirror 35, and it successively passesthrough a concave conical optical member 36A in which the light-incomingplane is a flat surface and the light-outgoing plane is an externallyconcave conical surface and through a convex conical optical member 36Bin which the light-incoming plane is an externally convex conicalsurface and the light-outgoing plane is a flat surface. After that, theP-polarized first light flux passes through a polarizing beam splitter40. On the other hand, a S-polarized second light flux, which hasreflected by the polarizing beam splitter 33, successively passesthrough a convex conical optical member 34A in which the light-incomingplane is a flat surface and the light-outgoing plane is an externallyconvex conical surface and through a convex conical optical member 34Bin which the light-incoming plane is an externally convex conicalsurface and the light-outgoing plane is a flat surface. After that, theS-polarized second light flux passes along a mirror 39, and it isreflected by the polarizing beam splitter 40. The first light flux andthe second light flux, which are coaxially combined by the polarizingbeam splitter 40, pass through a ¼ wavelength plate 41, and they areconverted into the laser beam LB1 which is the circularly polarizedlight beam. The laser beam LB1 comes into a beam expander 42A, 42Bcomposed of lenses 42A, 42B. Convex or concave conical prisms (axicons)can be used as the conical optical members 34A, 34B, 36A, 36B.

In this arrangement, a fixed unit 37A is constructed by the ¼ wavelengthplate 32, the polarizing beam splitter 33, the mirror 35, and the twoconical optical members 34A, 36A. A movable unit 38B is constructed bythe two conical optical members 34B, 36B, the mirror 39, the polarizingbeam splitter 40, and the ¼ wavelength plate 41. The movable unit 38B ismovable along the optical axis of the laser beam LB1 with respect to thefixed unit 37A by the aid of an unillustrated slide unit. The fixed unit37A and the movable unit 38B constitute a beam-shaping system. Thelight-outgoing plane for the laser beam LB1 from the modifiedillumination mechanism 19 is optically conjugate with the light-incomingplane of the fly's eye lens 25 shown in FIG. 2. The first lens 42B ofthe beam expander 42A, 42B is arranged movably along the optical axis bythe aid of an unillustrated slide unit. The expansion/contractionmagnification for the cross-sectional configuration of the laser beamLB1 can be controlled by driving the lens 42B. The operation of theslide units is controlled by the illumination control system 10 shown inFIG. 2.

The operation of the fixed unit 37A, the movable unit 38B, and the beamexpander 42A, 42B will now be explained with reference to FIGS. 3 and 4.

With reference to FIG. 3(a), the movable unit 38B is moved to a positionwhich is closest to the fixed unit 37A. The concave light-outgoing planeof the conical optical member 36A makes tight contact with the convexlight-incoming plane of the conical optical member 36B. Therefore,assuming that the intensity distribution in the cross section of theincoming laser beam LB is a Gaussian distribution, the intensitydistribution, which is obtained in the cross section (X direction is thedirection along the cross section) of the first light flux I1 passedthrough the conical optical members 36A, 36B as it is after beingtransmitted through the polarizing beam splitter 33, is a Gaussiandistribution which is convex about the center of the optical axis asshown in FIG. 3(b). On the other hand, the spacing distance between theconical optical members 34A, 34B is set so that the central portion andthe peripheral portion of the intensity distribution of the incomingsecond light flux I2 are inverted. The intensity distribution, which isobtained in the cross section of the second light flux I2 passed throughthe conical optical members 34A, 34B, is a distribution which isobtained by inverting the Gaussian distribution upside down as shown inFIG. 3(c). Therefore, the intensity distribution, which is obtained inthe cross section of the laser beam LB1 obtained by combining the firstlight flux I1 and the second light flux I2 by the polarizing beamsplitter 40, is approximately flat as shown in FIG. 3(d). The laser beamLB1 is converted by the beam expander 42A, 42B into the laser beam LB2in which the cross-sectional configuration is magnified with a variablemagnification. The laser beam LB2 shown in FIG. 3 is used for theordinal illumination. However, if it is intended to perform the small σvalue illumination in which the σ value as the coherence factor isdecreased, it is enough that the spacing distance of the beam expander42A, 42B is narrowed (magnification is decreased) to decrease the outerdiameter of the laser beam LB2. That is, the σ value (angular apertureof the laser beam on the reticle) as the coherence factor can be changedcontinuously and arbitrarily by adjusting the spacing distance of thebeam expander 42A, 42B.

Assuming that the intensity distribution in the cross section of thelaser beam radiated from an excimer laser light source is a Gaussiandistribution in a predetermined direction, the intensity distributioncan be regarded to be approximately flat in a direction perpendicularthereto. Therefore, a “wedge-shaped” or cylindrical lens-shaped opticalmember, which has no refraction effect in a direction perpendicular tothe plane of paper of FIG. 3, may be used in place of the conicaloptical members 34A, 34B, 36A, 36B of this embodiment.

On the other hand, FIG. 4(a) shows an arrangement in which the movableunit 38B is moved in the direction to make separation from the fixedunit 37A. In FIG. 4(a), the intensity distribution of the first lightflux I1 passed through the conical optical members 36A, 36B is anannular Gaussian distribution in which the intensity is approximatelyzero in the vicinity of the optical axis as shown in FIG. 4(b). Theintensity distribution of the second light flux I2 passed through theconical optical members 34A, 34B is such an anuular distribution thatthe Gaussian distribution is inverted upside down in which the intensityis approximately zero in the vicinity of the optical axis as shown inFIG. 4(c). Therefore, the intensity distribution of the laser beam LB1obtained by combining the first light flux I1 and the second light fluxI2 by the polarizing beam splitter 40 is a substantially flat annulardistribution as described in FIG. 4(d). In this case, the outer diameterof the laser beam LB1 is enlarged as compared with the case shown inFIG. 3(a). Therefore, if it is intended to decrease the outer diameterof the laser beam LB1, the spacing distance of the beam expander 42A,42B is narrowed to decrease the magnification of the laser beam LB2 tobe finally radiated.

The laser beam LB2 shown in FIG. 4 is used when the annular illuminationas an example of the modified illumination is performed. The conditionfor the annular illumination (for example, the outer diameter, the innerdiameter, and the annular ratio of the secondary light source) can bechanged continuously and arbitrarily by only adjusting the spacingdistance between the movable unit 38B and the fixed unit 37A or by usingthe adjustment of the spacing distance between the movable unit 38B andthe fixed unit 37A and the adjustment of the spacing distance of thebeam expander 42A, 42B in combination.

Further, the laser beam LB2 shown in FIG. 4 can be also used when aplurality of (for example, four of) secondary light sources, which areeccentric from the optical axis on the pupil plane of the illuminationoptical system, for example, on the focal plane of the fly's eye lens 25on the light-outgoing side, are used, i.e., when the modifiedillumination in the narrow sense is performed. Also when the pluralityof eccentric secondary light source are used as described above, thefinal distribution of the secondary light sources is set by thecorresponding aperture diaphragm included in the diaphragm-switchingmember 27. Therefore, no trouble occurs even when the distribution isannular at the stage at which the light is radiated from the modifiedillumination mechanism 19. When the annular distribution is prepared, anadvantage is obtained such that the light amount loss is decreased atthe stage of the aperture diaphragm. However, for example, in order togenerate an illumination light beam which is uniformly distributed, forexample, over eccentric four areas even at the stage at which the lightis radiated from the modified illumination mechanism 19, opticalmembers, in each of which the light-outgoing plane or the light-incomingplane is quadrangular pyramid-shaped (pyramid type), may be used inplace of the conical optical members 34A, 34B, 36A, 36B. Accordingly, itis possible to further reduce the light amount loss.

In this case, an arrangement may be available, in which the conicaloptical member for forming the light intensity distribution shown inFIGS. 3(d) and 4(d) and the quadrangular pyramid-shaped optical memberare exchangeable depending on the illumination condition. In addition tothe arrangement shown in FIG. 3(a), for example, a diffracting opticalelement for the modified illumination may be arranged on thelight-incoming side with respect to the polarizing beam splitter 33. Anillumination light beam, which is distributed over four areas, may begenerated at the stage at which the light comes into the modifiedillumination mechanism 19. In this case, it is desirable that thediffracting optical element for the modified illumination is exchangedwith another optical element (for example, a diffracting optical elementfor distributing the illumination light beam over a circular area or anannular area) during the ordinary illumination and the annularillumination.

As described above, according to the modified illumination mechanism 19of this embodiment, the flat circular illuminance distribution and theflat annular illuminance distribution can be switched by controlling thespacing distance of the two pairs of the conical optical members.Therefore, it is possible to effect the ordinary illumination and themodified illumination (including the annular illumination) whileextremely decreasing the light amount loss. Further, it is possible toswitch the σ value of the illumination optical system in the state inwhich there is little light amount loss, by switching the magnificationof the laser beam LB2 by using the beam expander 42A, 42B.

In the arrangement shown in FIG. 3(a), the beam expander 42A, 42B isarranged on the light-outgoing side of the modified illuminationmechanism 19 to adjust (especially enlarge) the light flux diameter(magnification) of the laser beam LB1. Therefore, the followingadvantage is obtained. That is, it is enough that the respective opticalelements for constructing the modified illumination mechanism 19 aresmall, and it is possible to realize the small size as a whole. Thelight flux diameter of the laser beam LB1 may be also reduced byproviding, for example, a zoom optical system, in place of the beamexpander 42A, 42B. A zoom optical system may be provided on thelight-incoming side of the modified illumination mechanism 19 in placeof or in addition to the beam expander 42A, 42B (or the zoom opticalsystem described above) arranged on the light-outgoing side of themodified illumination mechanism 19 to continuously change the light fluxdiameter (magnification) of the laser beam LB coming into the modifiedillumination mechanism 19 (conical optical members 34A, 36A). In thiscase., it is possible to change the formation conditions, i.e., theouter diameter, the inner diameter, and the annular ratio (ratio betweenthe outer diameter and the inner diameter) mutually independently,especially when the intensity distribution of the laser beam LB1 isprescribed to be annular in the cross section by using the adjustment ofthe zoom optical system and the adjustment of the spacing distancebetween the fixed unit 37A and the movable unit 38B in combination.

In this embodiment, the diaphragm-switching member 27 is provided toexchange the aperture diaphragm. However, it is not necessarilyindispensable to provide the diaphragm-switching member 27, because themodified illumination mechanism 19 can be used to change the intensitydistribution of the laser beam on the pupil plane of the illuminationoptical system. However, even in this case, it is desirable to arrangean aperture diaphragm for defining the maximum range for allowing thelaser beam to successfully pass on the pupil plane of the illuminationoptical system, i.e., the numerical aperture of the illumination opticalsystem to avoid any occurrence of flare or the like. When the mechanismfor exchanging the conical optical members 34A, 34B, 36A, 36B with thequadrangular pyramid-shaped optical members described above is notprovided, it is impossible to realize the modified illumination in thenarrow sense for forming the plurality of secondary light sources whichare eccentric from the optical axis of the illumination optical system.Accordingly, it is desirable that a shielding plate or a dimming plate(aperture diaphragm) for partially shielding or dimming the laser beamwith the illuminance distribution defined to be annular by the modifiedillumination mechanism 19 can be arranged, for example, closely to thelight-outgoing plane of the fly's eye lens 25 only when the modifiedillumination in the narrow sense is realized.

A modified illumination mechanism 19A as shown in FIG. 5 can be alsoused in place of the modified illumination mechanism 19. With referenceto FIG. 5, it is assumed that the illuminance distribution in the crosssection perpendicular to the optical axis of the laser beam LB on alight-incoming plane 48 is approximately square as indicated by ahatched area 50. In this illustrative arrangement, a slide member 46 isarranged movably to traverse the optical path of the laser beam LB.Those installed on four apertures of the slide member 46 are a phaseplate 47A for the ordinary illumination, a phase plate 47B for theannular illumination, a phase plate 47C for the modified illumination inthe narrow sense based on the use of eccentric four secondary lightsources, and a phase plate 47D for the small a value. Each of the phaseplates 47A to 47D is constructed such that a large number of finediffraction gratings of the phase type are formed in a predeterminedarrangement on a substrate which is transmissive with respect to thelaser beam LB.

It is assumed that the light-outgoing plane 49 shown in FIG. 5 isconjugate with the light-incoming plane of the fly's eye lens 25 shownin FIG. 2. When the slide member 46 is driven to install the phase plate47A on the optical path of the laser beam LB, the illuminancedistribution in the plane perpendicular to the optical axis on thelight-outgoing plane 49 of the laser beam LB1 transmitted through thephase plate 47A is circular as indicated by a hatched area 51A. When thephase plates 47B, 47C, 47D are installed on the optical path of thelaser beam LB respectively, the illuminance distributions of the laserbeam LB1 on the light-outgoing plane 49 reside in an annular area,eccentric four areas, and a small circular area as indicated by areas51B to 51D respectively. The arrangement of the diffraction grating ineach of the phase plates 47A to 47D is set so that the illuminancedistribution is approximately uniform in each of the areas 51A to 51D.Accordingly, the ordinary illumination and the modified illumination canbe switched to one another without causing any substantial loss of thelight amount of the incoming laser beam LB.

In addition to the arrangement shown in FIG. 5, for example, the pair ofconical prisms (axicons) described above may be arranged so that theannular area and the eccentric four areas are movable in the radialdirection about the center of the optical axis of the illuminationsystem.

Each of the phase plates 47A to 47D described above is constructed suchthat a plurality of minute phase patterns or minute transmittancepatterns are arranged on a substrate which is substantially transparentwith respect to the exposure light beam. Those usable as the materialfor the substrate include, for example, fluorite (CaF₂) and syntheticquartz doped with fluorine. As described above, in this embodiment, thephase plate 47A to 47D is used for the diffracting optical element(Diffracted Optical Element, hereinafter referred to as “DOE”). However,any one other than the phase plate may be used as DOE provided that thelight is diffracted depending on the difference, for example, in phase,transmittance, or refractive index. When DOE is used, the followingeffect is obtained, because it is possible to decrease the number ofoptical parts. That is, the arrangement of the illumination opticalsystem can be simplified, and the coherence of the exposure light beamcan be reduced to improve the uniformity of the illuminance distributionon the reticle. Alternatively, for example, the following arrangementmay be adopted. That is, when the full field exposure (static exposure)and the scanning exposure are switched to one another, the opticalintegrator is changed depending on the change of the illumination areaon the reticle. DOE (for example, the phase plate) may be exchanged withanother DOE when the change is performed. Further, DOE can be also usedas an optical integrator (uniformizer or homogenizer). In this case, onestage or a plurality of stages of optical integrator or opticalintegrators may be constructed with only one or a plurality of DOE orDOE's. Alternatively, a plurality of stages of optical integrators maybe constructed by combining one DOE and a fly's eye lens or a rod lens(internal reflection type integrator).

The laser beam LB1, which has passed through the modified illuminationmechanism 19 shown in FIG. 3(a), is advanced via the beam expander 42A,42B toward the delay optical system 22 shown in FIG. 2. The structureand the function of the delay optical system 22 will be explained indetail below with reference to FIGS. 6 and 7.

FIG. 6(a) shows a plan view illustrating the delay optical system 22shown in FIG. 2. With reference to FIG. 6(a), the delay optical system22 comprises prism-shaped rod members each of which has a width H of oneside and which are transparent with respect to the incoming laser beamLB2, the rod members being arranged in a quadrilateral frame-shapedconfiguration. One of portions corresponding to apexes of the quadrangleis used as a light-incoming/outgoing plane 43 composed of a reflectingsurface which intersects the optical axis of the laser beam LB by 45°.An aperture (window) 44, which is composed of a square transmittingsection having a width h as viewed in the optical axis direction asshown in FIG. 6(c), is formed at a central portion of thelight-incoming/outgoing plane 43 (the center thereof is approximatelycoincident with the optical axis). The portions corresponding to theother three apexes of the quadrangle are used as reflecting surfaces M1,M2, M3 which intersect the optical axis by 45° respectively. All of theother outer circumferential portions of the delay optical system 22 areformed as reflecting surfaces. It is enough that a reflecting film of ametal film such as chromium, or a multilayered reflecting film is formedon each of the reflecting surfaces. However, for example, the totalreflection may be utilized for the side surfaces of the prism-shaped rodmember. Similarly, the total reflection surface may be also utilized asmirror surfaces M1 to M3.

It is necessary that the optical member for constructing the delayoptical system 22 has a good transmittance with respect to the laserbeam LB2 (exposure light beam). Such an optical member is exemplified asfollows. That is, when the laser beam LB2 is the KrF excimer laser(wavelength: 248 nm), it is possible to use, for example, fused quartzglass or synthetic quartz glass. When the laser beam LB2 is the ArFexcimer laser (wavelength: 193 nm), it is possible to use, for example,synthetic quartz glass or fluorite (CaF₂). When the laser beam LB2 isthe F₂ laser (wavelength: 157 nm), it is possible to use, for example,synthetic quartz glass doped with an impurity such as fluorine andfluorite or magnesium fluoride (MgF₂). When the laser beam LB2 has awavelength of not more than about 150 nm, it is possible to use, forexample, fluorite or magnesium fluoride. Even when the material having ahigh transmittance as described above is used for the delay opticalsystem 22, it is feared that the heat is generated when the laser beamLB2 repeatedly passes through the inside of the material. Accordingly,it is desirable that a cooling mechanism for circulating a coolingmedium, a heat-absorbing mechanism such as a Peltier element, or aheat-discharging mechanism such as a heat pipe is provided to verticallyinterpose the delay optical system 22 thereby so that the delay opticalsystem 22 is cooled.

The delay optical system 22 has the quadrilateral frame-shapedconfiguration. However, the delay optical system 22 may have atriangular frame-shaped configuration, or it may have a hexagonal orhigher polygonal frame-shaped configuration. Further, a member, which isobtained by forming a cylindrical optical member to have a ring-shapedconfiguration, may be used for the delay optical system 22. When such aring-shaped member is used, the window for allowing the laser beam tocome thereinto or outgo therefrom may be a reflecting section in ajoined plane which is formed obliquely at an intermediate portion of themember. It is possible to decrease the amount of use of the opticalmember even when the delay optical system 22 is allowed to have a largesize, by using the polygonal frame-shaped optical member or thering-shaped optical member as the delay optical system 22 as describedabove. For example, even when the expensive material such as fluoriteand magnesium fluoride is used as the optical material for the delayoptical system 22, it is enough to use a small amount of the materialfor the delay optical system 22 of this embodiment. Therefore, it ispossible to greatly reduce the production cost. Even when it isdifficult to produce large-sized satisfactory crystals as in magnesiumfluoride, an advantage is also obtained in that the delay optical system22 of this embodiment can be produced with ease by joining, for example,a plurality of prism-shaped (or columnar) members.

The delay optical system 22 may be constructed by combining a pluralityof mirrors to cover the optical path of the laser beam thereby withoutusing any refractive member. In this arrangement, a high transmittancecan be obtained such that the interior is purged with a so-called inertgas such as nitrogen gas and helium gas having a high transmittance withrespect to the laser beam in the ultraviolet region, or the interior isevacuated to vacuum. Any of the front surface mirror and the backsurface mirror may be used for the mirror to be used when the pluralityof mirrors are combined to construct the delay optical system 22 asdescribed above. Further, the delay optical system 22 may be constructedwith a refractive member and a hollow section composed of a plurality ofreflecting members (mirrors or the like). That is, a part or all of thedelay optical system 22 may be hollow.

The laser beam LB2, which comes into the delay optical system 22, iscollected. Therefore, the laser beam LB2 can be considered as anaggregate of a variety of light fluxes having angular apertures rangingfrom 0° (i.e., light flux parallel to the optical axis) to apredetermined maximum value. If the light-collecting point of the laserbeam LB is located on the aperture 44 of the delay optical system 22 orat the inside of the delay optical system 22, it is feared that theoptical material for constructing the delay optical system 22 may bedamaged due to the concentration of the intense thermal energy.Accordingly, in order to protect the optical material, thelight-collecting point of the laser beam LB2 is actually positioned inthe gas (or in the vacuum in some cases) existing at the outside of theaperture 44. The light flux, which is widened or spread to some extentthereafter, comes into the aperture 44. However, for the convenience ofexplanation, FIGS. 6 and 7 are depicted assuming that the laser beam LB2is collected on the aperture 44.

The laser beam LB2, which comes into the aperture 44 of the delayoptical system 22, is successively reflected in a closed loop-shapedform by the mirrors M1, M2, M3, and the light beam LB2 is directedtoward the light-incoming/outgoing plane 43. Only the light fluxes,which are accommodated in the aperture 44, are radiated through theaperture 44 to the outside. The remaining light fluxes are advancedagain in the loop-shaped optical path in the delay optical system 22.The light fluxes, which are consequently accommodated in the aperture 44during the process of passage twice, three times, . . . through theloop-shaped optical path, are also radiated through the aperture 44 tothe outside. The light fluxes, which are obtained by superimposing theplurality of light fluxes radiated through the aperture 44, form thelaser beam LB3. In this arrangement, the number of times of passage ofeach of the light fluxes for constructing the laser beam LB2 through thedelay optical system 22 is determined depending on the angular apertureof each of the light fluxes. Therefore, explanation will be made belowfor the relationship between the angular aperture of the light flux andthe number of times of passage of the light flux through the delayoptical system 22. The “angular aperture” of the predetermined lightflux in this embodiment represents the angle which is formed by thelight flux with respect to the optical axis in the delay optical system22.

The delay optical system 22 is equivalent to an arrangement obtained bysuccessively connecting trapezoidal optical members 45A, 45B, 45C, 45Dvia the mirrors M1, M2, M3 and the light-incoming/outgoing plane 43.Therefore, for the convenience of explanation, as shown in FIG. 6(b),the delay optical system 22 is regarded to be an optical system in whichthe optical members 45A to 45D are arranged in series.

With reference to FIG. 6(b), the light flux having an angular apertureθ, which originates from the laser beam LB2 incoming into the aperture44 of the light-incoming/outgoing plane 43 of the delay optical system22, is radiated from the aperture 44 after passing through the opticalpath having a length L in the delay optical system 22 once. In FIG.6(b), the angular aperture θ is large for the purpose of bettercomprehension. However, actually, as shown in FIG. 6(d) which isobtained by reducing those shown in FIG. 6(b) in the optical axisdirection and connecting a plurality of them repeatedly, most of thelight fluxes have the angular aperture ranging from 0 to arctan(H/(2L))(rad) provided that H represents the width of the delay optical system22. The light flux 52A, which has the angular aperture θ approximate to0, is radiated as it is from the aperture 44. The light flux 52B, whichhas the angular aperture θ that is approximately arctan(H/(2L)), isradiated from the aperture 44 after passing through the delay opticalsystem 22 twice. The light fluxes 52C, 52D, . . . , which have theangular apertures θ that are smaller than arctan(H/(2L)), are radiatedfrom the aperture 44 after passing through the delay optical system 22three times, four times, . . . respectively. That is, the number oftimes of passage n of the light flux 52A to 52D through the delayoptical system 22 is 1 to 4. The number of times of passage (number oftimes of looping) is the value which can be appropriately set dependingon, for example, the width h of the aperture 44, the angular aperture θ,the length L of the optical path, and the width H of the delay opticalsystem 22.

In this embodiment, the length L of the optical path in the delayoptical system 22 is set so that the coherence almost disappears betweenthe light fluxes passed through the delay optical system 22 differentnumbers of times. That is, assuming that ε represents the refractiveindex of the delay optical system 22 with respect to the laser beam LB2,the optical path length ε·L for making a round trip in the delay opticalsystem 22 is set to be not less than the coherence length CL of thelaser beam LB2. In this case, assuming that λ₀ represents the centralwavelength of the laser beam LB2 in vacuum and Δλ represents the halfvalue width of the wavelength, the coherence length CL is approximatelyrepresented as follows. The half value width Δλ is a value which isdetermined depending on the temporal coherence of the laser beam LB2.

ε·L≧CL=λ ₀ ²/Δλ  (4)

However, the longer the length L is, the more difficult the productionof the delay optical system 22 is. Therefore, it is desirable that theoptical path length ε·L is not more than about twice the coherencelength CL. When the laser beam LB2 of this embodiment is thenarrow-banded KrF excimer laser beam, the coherence length CL is 153 mmor 410 mm provided that the central wavelength λ₀ is 248 nm and the halfvalue width Δλ of the wavelength is 0.4 pm or 0.15 pm respectively.Therefore, assuming that the coherence length CL is about 450 mm with acertain margin and the refractive index ε of the delay optical system 22is about 1.5, it is enough that the length L of the optical path is notless than about 300 mm and not more than about 600 mm in order that theexpression (4) is satisfied and the optical path length ε·L is not morethan about twice the coherence length CL. Therefore, the delay opticalsystem 22 may have a rectangular frame-shaped configuration in which thewidth of one side is not less than about 75 mm and not more than about150 mm. Accordingly, the temporal coherence of the laser beam LB3outgoing from the delay optical system 22 is greatly lowered as comparedwith the incoming laser beam LB2. In this embodiment, the light fluxes,which pass through the delay optical system 22 three or more times, arealso included. Therefore, even when the expression (4) is notnecessarily satisfied, i.e., even when the optical path length ε·L isshorter than the coherence length CL, the effect to lower the temporalcoherence is obtained to some extent.

The cross-sectional area of the delay optical system 22 is H², and thearea of the aperture 44 is h². Therefore, the incoming laser beam LB2 isdivided (subjected to wave front division) approximately into h²/H²(=(h/H)×(h/H)) when the laser beam LB2 passes through the delay opticalsystem 22 once. When the number of wave front division is larger, thenthe temporal coherence is lowered, and the uniformity of the illuminancedistribution is improved. In this embodiment, for example, the width Hof the delay optical system 22 is set to be about 30 to 100 mm, and thewidth h of the aperture 44 is set to be about 3 to 10 mm. That is,h²/H², which is the number of wave front division, is set to be about{fraction (1/100)}. However, it is desirable that the number of wavefront division is about {fraction (1/50)} to {fraction (1/200)}.Accordingly, the delay optical system 22 can also serve as a one-stageoptical integrator (uniformizer or homogenizer).

Next, explanation will be made in detail for the relationship among theangular aperture θ of each of the light fluxes for constructing thelaser beam LB2 incoming into the delay optical system 22, the length Lof the optical path of the delay optical system 22, the width H of thedelay optical system 22, the width h of the aperture 44, and the numberof times n of passage of the light flux through the delay optical system22. At first, as having been explained, FIG. 6(d) corresponds to thecase in which the width h of the aperture 44 is approximately 0, and thelight flux, which passes through the delay optical system 22 a pluralityof numbers of times, is expressed by the light flux which passes throughthe optical system obtained by connecting a plurality of the delayoptical systems 22 in series. In this case, the numbers of times n, withwhich the light fluxes 52A to 52D having the angular apertures θ of thepredetermined values respectively pass through the delay optical system22, are 1 to 4.

On the other hand, FIG. 7(a) corresponds to a case in which the width hof the aperture 44 has a predetermined width on condition that aplurality of the delay optical systems 22 are connected in series. Inthis case, the numbers of times n, with which the light fluxes 52A to52F having the angular apertures θ of the predetermined values within apredetermined range respectively pass through the delay optical system22, are 1 to 6. FIG. 7(b) shows a situation in which the plurality oflight fluxes having the different numbers of times n of passage throughthe delay optical system 22 as described above are radiated as the laserbeam LB3 from the aperture 44. As described above, the light flux havingthe predetermined angular aperture repeatedly passes through the delayoptical system 22 in accordance with the reflection at the outercircumferential surfaces of the delay optical system 22, and thus thewave front division is effected.

In the following description, the computer simulation is used todetermine and demonstrate the result of the way of change of the numberof times n of passage through the delay optical system 22 depending onthe angular aperture θ for a case in which the length L of the opticalpath of the delay optical system 22 is 300 mm, the width H of the delayoptical system 22 is 55 mm, the width h of the aperture 44 is 5 mm, andthe maximum value θmax of the angular aperture θ of the incoming laserbeam LB2 is an angle to satisfy (L·tanθmax=H), i.e., 10.39°. In thiscase, the number N (=n−1), which is obtained by subtracting 1 from thenumber of times n of passage, is called “number of repeating times”.Table 1 resides in a case in which the number of repeating times is 0,1, 2, . . . , 29, 30 to express the angular aperture θ (°) of the lightflux, the spacing distance from the optical axis of the positionobtained when the light flux passes through the delay optical system 22once (hereinafter referred to as “beam position”)×(mm), and the totallength ΣL (mm) of the optical path through which the light flux passesuntil the light flux is radiated from the delay optical system 22. Thebeam position x corresponds to the position at which each of the lightfluxes makes traverse on the straight line on which the number of timesn of passage is 1 as shown in FIG. 6(d). In Table 1, a light fluxincoming at an angular aperture θ=0° is radiated at a total length ofoptical path ΣL=300 mm and N=0, and a light flux incoming at an angularaperture θ≈5.24° is radiated at a total length of optical path ΣL=600 mmand N=1.

TABLE 1 N θ Position X ΣL 0 0 0 300 1 5.237477 27.5 600 2 2.62422113.704167 900 3 1.750160 9.1361111 1200 4 1.312799 6.8520833 1500 51.050305 5.4816667 1800 6 0.875284 4.5880558 2100 7 0.750259 3.91547622400 8 0.656486 3.4260417 2700 9 0.583548 3.0453704 3000 10 0.5251972.7408333 3300 11 0.477454 2.4916667 3600 12 0.437668 2.2840278 3900 130.404002 2.1083333 4200 14 0.375146 1.9577381 4500 15 0.350137 1.82722224800 16 0.328254 1.7130208 5100 17 0.308945 1.6122549 5400 18 0.2917821.5226852 5700 19 0.276425 1.4425439 6000 20 0.262604 1.3704167 6300 210.250099 1.3051587 6600 22 0.238731 1.2458333 6900 23 0.228352 1.19166677200 24 0.218837 1.1420139 7500 25 0.210084 1.0963333 7800 26 0.2020041.0541667 8100 27 0.194522 1.0151235 8400 28 0.187575 0.978869 8700 290.181107 0.9451149 9000 30 0.175070 0.9136111 9300

With only FIG. 1, it is unclear what is the angular aperture θ at whichthe light flux is radiated from the aperture 44 having the width h andwhat is the number of repeating times N (=n−1) the light flux isradiated. Accordingly, Table 2 shows the result of calculation todetermine how many times the light flux having the angular aperture θpasses through the delay optical system 22 to be finally radiated fromthe aperture 44.

In Table 2, the vertical axis represents the combination of the beamposition x (mm) of the light flux passed through the delay opticalsystem 22 once and the length y (mm) of the optical path along theoptical axis along which the light flux passes until the light fluxreturns to the optical axis (center) of the delay optical system 22. Thehorizontal axis represents the number of times n of passage of the lightflux through the delay optical system 22. Table 2 shows the result ofcalculation for the angular aperture θ (°) corresponding to the values(x, y) of the vertical axis and the value n of the horizontal axis. Inthis case, the length y of the optical path along which the light fluxpasses is close to an integral multiple of the length L (300 mm in thiscase) of the optical path of the delay optical system 22. Further, onlythe light flux, which passes through the area having the width h in thevicinity of the optical axis after being reflected at the outercircumferential surfaces of the delay optical system 22, is radiatedfrom the aperture 44 having the width h. This condition means, in Table2, the fact that the light flux having the angular aperture θ, whichcorresponds to the portion in which the beam position x is ±h/2 (±2.5 mmin this case) about the center of the portion in which the length y ofthe optical path is an integral multiple of 300 mm, is radiated from theaperture 44.

TABLE 2 x y n = 1 2 3 4 5 6 7 8 9 10 11 27.5 272.7273 0.55 B1.10 1.65C2.20 2.75 3.30 3.85 4.40 4.95 5.50 6.05 27 277.7778 0.54 B1.08 1.62C2.16 2.70 3.24 3.78 4.32 4.86 5.40 5.94 26.5 283.0189 0.53 B1.06 1.59C2.12 2.65 3.18 3.71 4.24 4.77 5.30 5.83 26 288.4615 0.52 B1.04 1.56C2.08 2.60 3.12 3.64 4.16 4.68 5.20 5.72 25.5 294.1176 0.51 B1.02 1.53C2.04 2.55 3.06 3.57 4.08 4.59 5.10 5.61 25 300 0.50 B1.00 C1.50 C2.022.50 3.00 3.50 4.00 4.50 5.00 5.50 24.5 306.1224 0.49 B0.98 C1.47 1.962.45 2.94 3.43 3.92 4.41 4.90 5.39 24 312.5 0.48 B0.96 C1.44 1.92 2.402.88 3.36 3.84 4.32 4.80 5.28 23.5 319.1489 0.47 B0.94 C1.41 1.88 2.352.82 3.29 3.76 4.23 4.70 5.17 23 326.087 0.46 B0.92 C1.38 1.84 2.30 2.763.22 3.68 4.14 4.60 5.06 22.5 333.3333 0.45 B0.90 C1.35 1.80 B2.25 2.703.15 3.60 4.05 4.50 4.95 22 340.9091 0.44 0.88 C1.32 1.76 B2.20 2.643.08 3.52 3.96 4.40 4.84 21.5 348.8372 0.43 0.86 C1.29 1.72 B2.15 2.583.01 3.44 3.87 4.30 4.73 21 357.1429 0.42 0.84 C1.26 1.68 B2.10 2.522.94 3.36 3.78 4.20 4.62 20.5 365.8537 0.42 0.82 C1.23 1.64 B2.05 2.462.87 3.28 3.69 4.10 4.51 20 375 0.40 C0.80 C1.20 1.60 B2.00 2.40 2.803.20 3.60 4.00 4.40 19.5 384.6154 0.39 C0.78 1.17 1.56 B1.95 2.34 2.733.12 3.51 3.90 4.29 19 394.7368 0.38 C0.76 1.14 1.52 B1.90 2.28 2.663.04 3.42 3.80 4.18 18.5 405.4054 0.37 C0.74 B1.11 1.48 B1.85 2.22 2.592.96 3.33 3.70 4.07 18 416.6667 0.36 C0.72 B1.08 1.44 1.80 2.16 2.522.88 3.24 3.60 3.96 17.5 428.5714 0.35 C0.70 B1.05 1.40 1.75 2.10 2.452.80 3.15 3.50 3.85 17 441.1765 0.34 C0.68 B1.02 1.36 1.70 2.04 2.382.72 3.06 3.40 3.74 16.5 454.5455 0.33 C0.66 B0.99 1.32 1.65 1.98 2.312.64 2.97 3.30 3.63 16 468.75 0.32 C0.64 B0.96 1.28 1.60 1.92 2.24 2.562.88 3.20 3.52 15.5 483.871 0.31 C0.62 B0.93 1.24 1.55 1.86 2.17 2.482.79 3.10 3.41 15 500 0.30 C0.60 B0.90 B1.20 C1.50 1.80 2.10 2.40 2.703.00 3.30 14.5 517.2414 0.29 0.58 0.87 B1.16 C1.45 1.74 2.03 2.32 2.612.90 3.19 14 535.7143 0.28 0.56 0.84 B1.12 C1.40 1.68 1.96 2.24 2.522.80 2.08 13.5 555.5556 0.27 0.54 0.81 B1.08 C1.35 1.62 1.89 2.16 2.432.70 2.97 13 576.9231 0.26 0.52 C0.78 B1.04 C1.30 1.56 1.82 2.08 2.342.60 2.86 12.5 600 0.25 0.50 C0.75 B1.00 1.25 1.50 1.75 2.00 2.25 2.502.75 12 625 0.24 0.48 C0.72 B0.96 1.20 1.44 1.68 1.92 2.16 2.40 2.6411.5 652.1739 0.23 0.46 C0.69 B0.92 1.15 1.38 1.61 1.84 2.07 2.30 2.5311 681.8182 0.22 0.44 C0.66 B0.88 1.10 1.32 1.54 1.76 1.98 2.20 2.4210.5 714.2857 0.21 0.42 C0.63 B0.84 B1.05 1.26 1.47 1.68 1.89 2.10 2.3110 750 0.20 0.40 C0.60 0.80 B1.00 1.20 1.40 1.60 1.80 2.00 2.20 9.5789.4737 0.19 0.38 C0.57 0.76 B0.95 1.14 1.33 1.52 1.71 1.90 2.09 9833.3333 0.18 0.36 C0.54 C0.72 B0.90 1.08 1.26 1.44 1.62 1.80 1.98 8.5882.3529 0.17 0.34 0.51 C0.68 B0.85 1.02 1.19 1.36 1.53 1.70 1.87 8937.5 0.16 0.32 0.48 C0.64 B0.80 0.96 1.12 1.28 1.44 1.60 1.76 7.5 10000.15 0.30 0.45 C0.60 B0.75 B0.90 1.05 1.20 1.35 1.50 1.65 7 1071.4290.14 0.28 0.42 C0.56 0.70 B0.84 0.98 1.12 1.26 1.40 1.54 6.5 1153.8460.13 0.26 0.39 C0.52 0.65 B0.78 0.91 1.04 1.17 1.30 1.43 6 1250 0.120.24 0.36 C0.48 C0.60 B0.72 B0.84 0.96 1.08 1.20 1.32 5.5 1363.636 0.110.22 0.33 0.44 C0.55 0.66 B0.77 0.88 0.99 1.10 1.21 5 1500 0.10 0.200.30 0.40 C0.50 C0.60 B0.70 B0.80 0.90 1.00 1.10 4.5 1666.667 0.09 0.180.27 0.36 0.45 C0.54 0.63 B0.72 0.81 0.90 0.99 4 1875 0.08 0.16 0.240.32 0.40 C0.48 C0.56 B0.64 B0.72 0.80 0.88 3.5 2142.857 0.07 0.14 0.210.28 0.35 C0.42 C0.49 0.56 B0.63 0.70 0.77 3 2500 0.06 0.12 0.18 0.240.30 0.36 C0.42 C0.48 B0.54 B0.60 0.66 2.5 3000 A0.05 0.10 0.15 0.200.25 0.30 0.35 C0.40 0.45 B0.50 0.55 2 3750 A0.04 0.08 0.12 0.18 0.200.24 0.28 0.32 0.36 0.40 0.44 1.5 5000 A0.03 0.06 0.09 0.12 0.15 0.180.21 0.24 0.27 0.30 0.33 1 7500 A0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.160.18 0.20 0.22 0.5 15000 A0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.090.10 0.11 0 300 A0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

It is possible to determine what kind of light flux is radiated from theaperture 44 having the width h after passing through the delay opticalsystem 22 how many times, by selecting all of the portions which satisfythe condition described above for each of the angular apertures θ inTable 2. When the width H of the delay optical system 22 is 55 mm, thelight flux having the angular aperture θ, which is affixed with thesymbol A or B just before, is radiated from the aperture 44. For thepurpose of reference, a condition has been also determined, in which thewidth of the delay optical system 22 is 1.5×H (i.e., 1.5×55=82.5 (mm)).As a result, it has been revealed that the light flux having the angularaperture θ, which is affixed with the symbol A or C, is radiated fromthe aperture 44 at the corresponding number of times n. That is, thelight flux having the angular aperture θ, which is affixed with thesymbol A, is common to the delay optical systems 22 having the differentwidths.

Next, Tables 3 to 5 show the results obtained by performing simulationfor the number of wave front division on the basis of the result shownin Table 2. The number of wave front division is determined by thelength L of the optical path, the distribution of the angular apertureof the incoming laser beam, and the value of the ratio h/H between thewidth h of the aperture 44 and the width H of the delay optical system22. The angular aperture distribution successfully corresponds to thedistribution of the position at which the laser beam, which has passedthrough the delay optical system 22 once, passes through in the crosssection of the delay optical system 22. Accordingly, it is assumed thatthe cross-sectional configuration of the delay optical system 22satisfies 1.5×H (=82.5 mm) in the lateral direction (designated as the Xdirection) and H (=55 mm) in the vertical direction (designated as the Ydirection). Further, it is assumed that the width of the aperture 44also satisfies 1.5×h (=7.5 mm) in the X direction and h (=5 mm) in the Ydirection. The origin of the coordinate (X, Y) is placed at the centerof the cross section of the delay optical system 22. The cross sectionof the delay optical system 22 is divided into eleven individuals in theX direction and the Y direction respectively by using the width of theaperture 44 as unit. Tables 3 and 4 show the results of the division inthe first quadrant (0<X<1.5·H/2, 0<Y<H/2) of the cross section of thedelay optical system 22.

That is, in Table 3, the area of 0<X<1.5·H/4 in the first quadrant ofthe cross section of the delay optical system 22 is divided by using theunit of the width of the aperture 44 in the X direction and the Ydirection respectively except for the portion of the aperture 44(portion having the width in the X direction of 1.5·h/2 and the width inthe Y direction of h/2). In Table 4, the area of 1.5·H/4<X<1.5·H/2 inthe first quadrant is divided in the X direction and the Y directionrespectively by using the unit of the width of the aperture 44. InTables 3 and 4, each of the divided areas is divided into six latticepoints in the X direction and the Y direction respectively to show thevalue of the total number of times n with which the light flux, whichhas passed through the delay optical system 22 once and which has passedthrough each of the lattice points described above, passes through thedelay optical system 22 until the light flux is radiated from theaperture 44 respectively. For example, an area of 0<X<1.5·h/2, 0<Y<h/2in Table 3 is an area in the aperture 44. Therefore, the number of timesn, with which the laser beam having passed through each of the latticepoints in the concerning area passes through the delay optical system22, is 1 respectively. The number of times n, with which the laser beamhaving passed through each of the lattice points in an area of0<X<1.5·h/2, 9h/2<Y<H/2 in Table 3 passes through the delay opticalsystem 22, is 2 respectively.

TABLE 3 X = 0 1.5 · h/2 1.5 · H/4 H/2 2 2 2 2 2 2 8 14 6 10 4 4 4 4 6 66 6 2 2 2 2 2 2 8 14 6 10 4 4 4 4 6 6 6 6 2 2 2 2 2 2 8 14 6 10 4 4 4 46 6 6 6 2 2 2 2 2 2 8 14 6 10 4 4 4 4 6 6 6 6 2 2 2 2 2 2 8 14 6 10 4 44 4 6 6 6 6 2 2 2 2 2 2 8 14 6 10 4 4 4 4 6 6 6 6 9h/2 5 5 5 5 5 5 40 3530 5 20 20 20 20 15 15 15 15 5 5 5 5 5 5 40 35 30 5 20 20 20 20 15 15 1515 5 5 5 5 5 5 40 35 30 5 20 20 20 20 15 15 15 15 5 5 5 5 5 5 40 35 30 520 20 20 20 15 15 15 15 3 3 3 3 3 3 24 21 6 15 12 12 12 12 3 3 3 3 3 3 33 3 3 24 21 6 15 12 12 12 12 3 3 3 3 3 3 3 3 3 3 24 21 6 15 12 12 12 123 3 3 3 3 3 3 3 3 3 24 21 6 15 12 12 12 12 3 3 3 3 3 3 3 3 3 3 24 21 615 12 12 12 12 3 3 3 3 4 4 4 4 4 4 8 28 12 20 4 4 4 4 12 12 12 12 4 4 44 4 4 8 28 12 20 4 4 4 4 12 12 12 12 4 4 4 4 4 4 8 28 12 20 4 4 4 4 1212 12 12 4 4 4 4 4 4 8 28 12 20 4 4 4 4 12 12 12 12 4 4 4 4 4 4 8 28 1220 4 4 4 4 12 12 12 12 4 4 4 4 4 4 8 28 12 20 4 4 4 4 12 12 12 12 5 5 55 5 5 40 35 30 5 20 20 20 20 15 15 15 15 5 5 5 5 5 5 40 35 30 5 20 20 2020 15 15 15 15 5 5 5 5 5 5 40 35 30 5 20 20 20 20 15 15 15 15 5 5 5 5 55 40 35 30 5 20 20 20 20 15 15 15 15 6 6 6 6 6 6 24 42 6 30 12 12 12 126 6 6 6 7 7 7 7 7 7 56 7 42 35 28 28 28 28 21 21 21 21 8 8 8 8 8 8 8 5624 40 8 8 8 8 24 24 24 24 9 9 9 9 9 9 72 63 18 45 36 36 36 36 9 9 9 9 1010 10 10 10 10 40 70 30 10 20 20 20 20 30 30 30 30 h/2 1 1 1 1 1 1 8 7 65 4 4 4 4 3 3 3 3 1 1 1 1 1 1 8 7 6 5 4 4 4 4 3 3 3 3 1 1 1 1 1 1 8 7 65 4 4 4 4 3 3 3 3 1 1 1 1 1 1 8 7 6 5 4 4 4 4 3 3 3 3 1 1 1 1 1 1 8 7 65 4 4 4 4 3 3 3 3 1 1 1 1 1 1 8 7 6 5 4 4 4 4 3 3 3 3 Y = 0

TABLE 4 X = 1.5 · H/4 1.5 · H/2 H/2 10 10 10 2 2 2 2 2 2 6 6 6 6 6 6 4 44 10 10 10 2 2 2 2 2 2 6 6 6 6 6 6 4 4 4 10 10 10 2 2 2 2 2 2 6 6 6 6 66 4 4 4 10 10 10 2 2 2 2 2 2 6 6 6 6 6 6 4 4 4 10 10 10 2 2 2 2 2 2 6 66 6 6 6 4 4 4 10 10 10 2 2 2 2 2 2 6 6 6 6 6 6 4 4 4 9h/2 5 5 5 10 10 1010 10 10 15 15 15 15 15 15 20 20 20 5 5 5 10 10 10 10 10 10 15 15 15 1515 15 20 20 20 5 5 5 10 10 10 10 10 10 15 15 15 15 15 15 20 20 20 5 5 510 10 10 10 10 10 15 15 15 15 15 15 20 20 20 15 15 15 6 6 6 6 6 6 3 3 33 3 3 12 12 12 15 15 15 6 6 6 6 6 6 3 3 3 3 3 3 12 12 12 15 15 15 6 6 66 6 6 3 3 3 3 3 3 12 12 12 15 15 15 6 6 6 6 6 6 3 3 3 3 3 3 12 12 12 1515 15 6 6 6 6 6 6 3 3 3 3 3 3 12 12 12 20 20 20 4 4 4 4 4 4 12 12 12 1212 12 4 4 4 20 20 20 4 4 4 4 4 4 12 12 12 12 12 12 4 4 4 20 20 20 4 4 44 4 4 12 12 12 12 12 12 4 4 4 20 20 20 4 4 4 4 4 4 12 12 12 12 12 12 4 44 20 20 20 4 4 4 4 4 4 12 12 12 12 12 12 4 4 4 20 20 20 4 4 4 4 4 4 1212 12 12 12 12 4 4 4 5 5 5 10 10 10 10 10 10 15 15 15 15 15 15 20 20 205 5 5 10 10 10 10 10 10 15 15 15 15 15 15 20 20 20 5 5 5 10 10 10 10 1010 15 15 15 15 15 15 20 20 20 5 5 5 10 10 10 10 10 10 15 15 15 15 15 1520 20 20 30 30 30 6 6 6 6 6 6 6 6 6 6 6 6 12 12 12 35 35 35 14 14 14 1414 14 21 21 21 21 21 21 28 28 28 40 40 40 8 8 8 8 8 8 24 24 24 24 24 248 8 8 45 45 45 18 18 18 18 18 18 9 9 9 9 9 9 36 36 36 10 10 10 10 10 1010 10 10 30 30 30 30 30 30 20 20 20 h/2 5 5 5 2 2 2 2 2 2 3 3 3 3 3 3 44 4 5 5 5 2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 5 5 5 2 2 2 2 2 2 3 3 3 3 3 3 44 4 5 5 5 2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 5 5 5 2 2 2 2 2 2 3 3 3 3 3 3 44 4 5 5 5 2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 Y = 0

In Tables 3 and 4, it can be regarded that the light fluxes of the laserbeams passing through the respective lattice points, for which the valueof the number of times n of passage through the delay optical system 22differs, scarcely cause interference with each other, because theoptical path length differs by not less than the coherence distance.That is, the light fluxes, which have different numbers of times n ofpassage, are substantially incoherent with each other. Accordingly, thenumber of light fluxes which are substantially incoherent with eachother is summarized in Table 5, on the basis of Tables 3 and 4.

In Table 5, n represents the entire number of times of passage throughthe delay optical system 22 of the light flux passing through each ofthe lattice points, NA represents the number of light fluxes (latticepoints) having the number of times of passage of n, and NB representsthe ratio of the number of light fluxes NA with respect to the totalnumber of light fluxes. According to Table 5, it is understood thatthere are twenty-two sets of the light fluxes which are substantiallyincoherent with each other. This means the fact that the temporalcoherence of the laser beam LB2 coming into the delay optical system 22is sufficiently reduced.

TABLE 5 n NA NB (%) 1 36 3 2 108 8 3 140 11 4 198 15 5 104 8 6 130 10 713 1 8 38 3 9 16 1 10 88 1 11 0 0 12 108 8 13 0 0 14 12 1 15 100 8 16 00 17 0 0 18 7 1 19 0 0 20 87 7 21 15 1 22 0 0 23 0 0 24 17 1 25 0 0 26 00 27 0 0 28 13 1 29 0 0 30 23 2 31 0 0 32 0 0 33 0 0 34 0 0 35 12 1 36 71 37 0 0 38 0 0 39 0 0 40 13 1 41 0 0 42 2 0 43 0 0 44 0 0 45 4 0 46 0 047 0 0 48 0 0 49 0 0 50 0 0 51 0 0 52 0 0 53 0 0 54 0 0 55 0 0 56 2 0 570 0 58 0 0 59 0 0 60 0 0 61 0 0 62 0 0 63 1 0 64 0 0 65 0 0 66 0 0 67 00 68 0 0 69 0 0 70 1 0 71 0 0 72 1 0 73 0 0 74 0 0 75 0 0 76 0 0 77 0 078 0 0 79 0 0 80 0 0 81 0 0 82 0 0 83 0 0 84 0 0 85 0 a 86 0 0 87 0 0 880 0 89 0 0 90 0 0 91 0 0 92 0 0 93 0 0 94 0 0 95 0 0 96 0 0 97 0 0 98 00 99 0 0 100 0 0

On the other hand, in the delay optical system 26 shown in FIG. 2 (FIG.6), the aperture 44, which is formed on the light-incoming/outgoingplane 43, is the window. However, in this arrangement, it is feared tocause any light amount loss of the incoming laser beam LB2 and theoutgoing laser beam LB3 due to the total reflection or the reflection atthe light-incoming/outgoing plane 43. In view of the above, explanationwill be made with reference to FIG. 8 for embodiments to lower the lightamount loss of the incoming laser beam and the outgoing laser beam.

At first, FIG. 8(a) shows a perspective view illustrating the appearanceof the delay optical system 22 shown in FIG. 2. With reference to FIG.8(a), the laser beam LB2 comes into the light-incoming/outgoing plane 43which is the inclined surface of the rectangular prism 22 a as a part ofthe delay optical system 22. The laser beam LB3 is radiated from thelight-incoming/outgoing plane 43. On this assumption, in the systemshown in FIG. 2, the light-incoming/outgoing plane 43 is used as thereflecting surface, and the rectangular aperture 44 is provided for apart thereof as shown in FIG. 8(b). In this system, the aperture 44,which is inclined by 45° with respect to the optical axis, is used forboth of the light-incoming window and the light-outgoing window. Theoutgoing laser beam LB3 is inclined with respect to the optical axis.Accordingly, in the example shown in FIG. 2, the wave front of the laserbeam LB3 is adjusted to be substantially perpendicular to the opticalaxis by using the aberration-correcting prism 23. In the case of thescanning exposure type as in this embodiment, it is desirable that thepitch direction of the interference fringe (speckle) having the highestcontrast formed in the illumination area of the reticle R is allowed tomake intersection by about 45° with respect to the scanning directionfor the reticle R, for the following reason. That is, by doing so, theinfluence of the uneven illuminance is mitigated owing to the averagingeffect in the scanning direction. In order to allow the pitch directionof the interference fringe on the reticle R to make intersection byabout 45° with respect to the scanning direction as described above, thedelay optical system 22 may be rotated by a predetermined angle aboutthe axis of the normal line of the aperture 44, and theaberration-correcting prism 23 may be also rotated, if necessary, withreference to FIG. 2.

On the other hand, in an example shown in FIG. 8(c), a small-sizedrectangular prism 44A is fixed on the light-incoming/outgoing plane 43of the rectangular prism 22 a. One of the two orthogonal surfaces of therectangular prism 44A is used as a light-incoming window for the laserbeam LB2, and the other is used as a light-outgoing window for the laserbeam LB3. This system is advantageous in that the light amount loss issmall for the incoming laser beam LB2 and the outgoing laser beam LB3.In an example shown in FIG. 8(d), a rectangular prism type recess 44Bhaving a small size is formed on the light-incoming/outgoing plane 43 ofthe rectangular prism 22 a. One of the two orthogonal surfaces of therecess 44B is used as a light-incoming window for the laser beam LB2,and the other is used as a light-outgoing window for the laser beam LB3.This system is also advantageous in that the light amount loss is smallfor the laser beams LB2, LB3. In the examples shown in FIGS. 8(c) and8(d), it is possible to further decrease the light amount loss of thelaser beam repeatedly passing through the delay optical system 22 byutilizing the light-incoming/outgoing plane 43 as a total reflectionplane.

Next, modified embodiments of the delay optical system 22 shown in FIG.2 will be explained with reference to FIG. 9.

A delay optical system 22A shown in FIG. 9(a) is constructed such thattwo rectangular prisms and two prism-shaped (or probably columnar) rodmembers are arranged to make tight contact in a ring-shapedconfiguration. The delay optical system 22A is advantageous toconsequently decrease the required space. In FIG. 9(b), a joined plane53 is provided obliquely at a central portion of a prism-shaped memberof a ring-shaped delay optical system 22B. A reflecting section isformed beforehand at a central portion of the joined plane 53 as thelight-incoming/outgoing plane. The reflecting section is used as alight-incoming window for the laser beam LB2, and the back surface ofthe reflecting section is used as a light-outgoing window for the laserbeam LB3. This exemplary arrangement is effective when there is no spacefor bending the laser beams LB2, LB3.

FIG. 9(d) shows an example in which an oblong aperture 44C, which servesas the window, is formed at a central portion of alight-incoming/outgoing plane 43 of a rectangular prism 22 a forconstructing a delay optical system 22. FIG. 9(d) shows an example inwhich a substantially square aperture 44D is formed as the window at aposition that is deviated (eccentric) from the center of alight-incoming/outgoing plane 43 of a rectangular prism 22 a. In theexamples shown in FIGS. 9(c) and 9(d), the reflection condition for theincoming laser beam differs between the vertical direction and thehorizontal direction. Therefore, it is possible to increase the numberof incoherent light fluxes, and it is possible to further reduce thetemporal coherence. Especially, in the example shown in FIG. 9(d), thereflection condition for the incoming laser beam differs for the foursurfaces in total of the upper and lower two surfaces and the right andleft two surfaces. Therefore, the effect to reduce the temporalcoherence is further enhanced.

FIG. 9(e) shows an example in which the entire surface of an inclinedsurface 43A of a rectangular prism 54 as a part for constructing a delayoptical system is a half mirror. The inclined surface 43A is used as thelight-incoming window and the light-outgoing window as a whole. In thisexample, most of the incoming laser beam is radiated after passingthrough the delay optical system three times. Therefore, the number ofincoherent light fluxes is small. However, an advantage is obtained suchthat the temporal coherence can be reduced with the simple arrangement.FIG. 9(f) shows an example in which the laser beam is allowed to comeinto the light-incoming/outgoing plane 43 of the delay optical system sothat there is no inclination of telecentricity. On the other hand, FIG.9(g) shows an example in which the laser beam is allowed to come intothe light-incoming/outgoing plane 43 with a predetermined inclination oftelecentricity. When the laser beam, which has a predeterminedinclination of telecentricity, is allowed to come into the delay opticalsystem as described above, it is possible to provide mutually differentreflection conditions in the delay optical system for the four surfaces,in the same manner as in the case in which the position of the aperture44 is eccentric as in the example shown in FIG. 9(d). Thus, it ispossible to greatly reduce the temporal coherence.

As described above, in this embodiment, the exposure method based on theuse of the KrF excimer laser has been explained. However, the delayoptical system 22 (or 22A, 22B or the like) will be also effective whenthe laser beam having coherence and having a shorter wavelength will beused as the exposure light beam in future, including, for example, theArF excimer laser (193 nm), the F₂ laser (157 nm), the Ar₂ laser beam(wavelength: 126 nm), the high harmonic wave of the YAG laser, and thehigh harmonic wave of the semiconductor laser. However, when the laserbeam having such a short wavelength is used, it is feared that the delayoptical system 22 is damaged due to any concentration of energy, or anycloudy substance, which is formed by the chemical reaction between thelaser beam and any minute organic substance or the like with which theatmosphere is contaminated, adheres to the light-incoming/outgoing plane43 of the delay optical system 22. Accordingly, the rectangular prism 22a (light-incoming/outgoing plane 43) of the delay optical system 22 maybe exchangeable. Alternatively, a transparent cover may be provided sothat the aperture 44 of the light-incoming/outgoing plane 43 is coveredtherewith in order to avoid any adhesion of the cloudy substance. Theinterior of the cover may be purged with a gas which is clear and whichhas a high transmittance with respect to the laser beam. In order toavoid any generation of organic matter or the like, it is desirable thatthe plurality of optical members (for example, rod members) forconstructing the delay optical system 22 are held in an integratedmanner with a press ring or the like, without using, for example, theadhesive or the filler.

There is such a possibility that the internal reflection effect isdecreased and a part of the light flux is lost at the connecting portion(bent portion) of the rod member for constructing the delay opticalsystem 22. The light amount loss is increased as the maximum angle ofthe angular aperture of the incoming laser beam LB2 becomes large.Therefore, it is also an important factor for enhancing the efficiencyof the use of the laser beam to design the delay optical system 22 sothat there is no bent portion at the position at which the light fluxhaving a large angular aperture is reflected at the inner surface of therod member.

When the interference fringes slightly remain on the reticle even whenthe delay optical system 22 of the embodiment described above isintroduced, the angle of inclination of the laser beam LB2 coming intothe delay optical system 22 with respect to the optical axis may beperiodically vibrated.

In the embodiment described above, the fly's eye lens 25 is used as theoptical integrator disposed on the light-outgoing side. However, a rodintegrator may be used in place of the fly's eye lens 25.

In the exemplary arrangement shown in FIG. 2, the delay optical system22 is arranged after the modified illumination mechanism 19. However,the delay optical system 22 may be arranged before the modifiedillumination mechanism 19. Further, when the intensity distribution ofthe laser beam LB is relatively flat, the modified illuminationmechanism 19 may be simplified.

Next, a second embodiment of the present invention will be explainedwith reference to FIGS. 10 to 16. Also in this embodiment, the presentinvention is applied to a case in which the exposure is performed with aprojection exposure apparatus based on the step-and-scan system. InFIGS. 10 and 11, components or parts corresponding to those shown inFIGS. 1 to 5 are designated by the same reference numerals, detailedexplanation of which will be omitted.

FIG. 10 shows a schematic arrangement of the projection exposureapparatus of this embodiment. With reference to FIG. 10, a laser beamLB, which has a narrow-banded wavelength as an illumination light beam(exposure light beam) for exposure and which is pulse-emitted from anexposure light source 9, comes into an illumination system 8. A KrFexcimer laser light source (oscillation wavelength: 248 nm), in whichthe oscillation wavelength width is narrow-banded, for example, intoabout 0.1 to 1 pm, is used as the exposure light source 9 of thisembodiment in the same manner as in the embodiment shown in FIG. 1.Other than the above, the present invention is also applicable to a caseto use an exposure light source for generating, for example, a laserbeam having high coherence such as ArF excimer laser (wavelength: 193nm) and F₂ laser (wavelength: 157 nm) as well as a high harmonic wavegenerator for YAG laser. Further, for example, an X-ray source can bealso used for the exposure light source 9. The light sources asdescribed above are pulse light sources.

The illumination system 8 is provided with an optical system forconverting the cross-sectional configuration of the incoming light fluxinto a desired shape in the same manner as in the embodiment shown inFIG. 1, a bent type rod-shaped optical member to serve as a multiplelight source-forming optical system or an optical integrator(uniformizer or homogenizer), a relay lens system, and a field diaphragm(reticle blind). The incoming laser beam LB is converted by theillumination system 8 into an illumination light beam IU which has apredetermined numerical aperture and which has a uniformized illuminancedistribution. The illumination light beam IU passes through a condenserlens system 7, and a pattern plane of a reticle R is illuminated with aslender illumination area having a rectangular configuration.

A storage unit 13 a, which is composed of, for example, a magnetic diskunit for storing, for example, the exposure condition, is connected to amain control system 13 of this embodiment. An uneven illuminance sensor2, which is composed of a photoelectric detector, is fixed in thevicinity of a wafer W on a wafer stage 1. As shown in FIG. 16(b), a pinhole-shaped light-receiving section 2 a is formed on the upper surfaceof the uneven illuminance sensor 2. A photoelectrically convertedsignal, which is obtained from the illumination light beam IU cominginto the light-receiving section 2 a, is supplied to the main controlsystem 13 shown in FIG. 10. The arrangement of the projection exposureapparatus shown in FIG. 10 other than the above is substantially thesame as the arrangement of the embodiment shown in FIG. 1, detailedexplanation of which will be omitted.

Next, explanation will be made in detail for the arrangement of theexposure light source 9 and the illumination system 8 of thisembodiment.

FIG. 11 shows the arrangement of the exposure light source 9 and theillumination system 8 shown in FIG. 10.

With reference to FIG. 11, the linearly polarized laser beam LB, whichis radiated from the exposure light source 9 constructed in the samemanner as the embodiment shown in FIG. 2, comes into the illuminationsystem 8.

In the illumination system 8, the laser beam LB is dimmed to have apredetermined illuminance (=average pulse energy per unit area xoscillation frequency) by the aid of a dimming unit 18. When the pulseemission type laser beam LB (illumination light beam IU) is used as theexposure light beam or the illumination light beam as in thisembodiment, it is necessary that the number of exposure pulses N (N isan integer) for each point on the wafer is not less than a predeterminedminimum number of pulses N_(min) which is determined depending on thedispersion of the pulse energy, in order to allow the totalized exposureamount at each point on the wafer to be included within an allowablerange with respect to a proper value.

Further, the proportional constant is previously determined between theilluminance of the laser beam LB on the light-incoming plane of thedimming unit 18 and the illuminance of the illumination light beam IU onthe wafer W for a case in which a standard aperture diaphragm is usedfor the illumination optical system. The proportional constant is storedin a storage unit in the illumination control system 10 shown in FIG.11. The illumination control system 10 sets the dimming ratio(transmittance) for the dimming unit 18 so that the postulated number ofexposure pulses N at each point on the wafer is not less than theminimum number of pulses N_(min), from the proportional constant, thepresent state of the aperture diaphragm, and the average pulse energy ofthe laser beam LB on the light-incoming plane.

With reference to FIG. 11, the laser beam LB, which has passed throughthe dimming unit 18, is radiated after being shaped by a modifiedillumination mechanism 19 so that the illuminance distribution in crosssection is in a predetermined state (for example, circular, annular, andeccentric plural light sources) and the illuminance distribution is asubstantially uniform distribution. A diaphragm-switching member 27,which is formed with a variety of aperture diaphragms (σ diaphragms) fordetermining the illumination condition (for example, ordinaryillumination, modified illumination, and illumination with smallcoherence factor (small σ value)) and the σ value, is rotatably arrangedin the vicinity of the light-outgoing plane of the modified illuminationmechanism 19, i.e., at the optical Fourier transformation plane (pupilplane) with respect to the pattern plane of the reticle R or in thevicinity thereof in this embodiment. The illumination control system 10rotates the diaphragm-switching member 27 by the aid of a driving motor26 to arrange a predetermined aperture diaphragm at the light-outgoingplane of the modified illumination mechanism 19. Thus, the illuminationcondition and the angular aperture of the laser beam (σ value) are set.

A laser beam LB2, which is radiated from the modified illuminationmechanism 19 to pass through the predetermined aperture diaphragm, iscollected by a light-collecting lens 21 and reflected by a mirror 55 toonce form a light source image (secondary light source). After that, thelaser beam LB2 behaves as a light flux having a predetermined angularaperture (σ value), and it comes into a bent type rod-shaped opticalmember 56 which serves as a multiple light source-forming optical systemof the present invention. The bent type rod-shaped optical member 56 isconstructed such that seven quadratic prism-shaped rod members 57A to57G, which have outer surfaces to serve as reflecting surfacesrespectively, are successively connected in a bent manner withintervening rectangular prism type mirror members 58A to 58F for bendingthe optical path by 90°. Each of the rod members 57A to 57G and themirror members 58A to 58F is formed of an optical material which istransmissive with respect to the laser beam LB2.

The laser beam LB2 is reflected by the mirror 55, and it comes into thefirst stage rod member 57A. The laser beam LB2 successively passesthrough the mirror member 58A, the rod member 57B, the mirror member58B, the rod member 57C, the mirror member 58C, the rod member 57D, themirror member 58D, the rod member 57E, the mirror member 58E, the rodmember 57F, the mirror member 58F, and the final stage rod member 57G inaccordance with the reflection (or total reflection) at the outersurfaces. The laser beam LB2 is radiated from a light-outgoing plane 76Gof the rod member 57G (as described in detail later on). The opticalpath, which ranges from the interior of the rod member 57A to theinterior of the rod member 57G, corresponds to the light-feeding opticalpath of the present invention. The light-outgoing plane 76G is set to besubstantially conjugate with the pattern plane of the reticle R as anillumination objective.

A movable blind 29B is arranged at a position which is close to thelight-outgoing plane 76G. A fixed blind 29A is arranged at a positionwhich is defocused by a predetermined amount from the movable blind 29B.In this arrangement, the slit-shaped illumination area on the reticle Ris defined by an aperture of the fixed blind 29A. The movable blind 29Bplays a role to shield the aperture of the fixed blind 29A in order thatany unnecessary pattern is transferred onto the wafer upon the start andthe end of the scanning exposure for each of the shot areas on thewafer. The illumination control system 10 controls the operation of themovable blind 29B by the aid of a driving unit 30 in accordance with thesynchronization information supplied from the main control system 13.

The illumination light beam IU, which has passed through the movableblind 29B and the aperture of the fixed blind 29A, illuminates thepattern plane of the reticle R via a relay lens system 31 and acondenser lens system 7. Although not shown, for example, a beamsplitter is arranged between the fixed blind 29A and the relay lenssystem 31. An integrator sensor is provided, which photoelectricallyconverts the illumination light beam incorporated by the aid of the beamsplitter. A detection signal obtained by the integrator sensor issupplied to the illumination control system 10. The relationship betweenthe detection signal of the integrator sensor and the illuminance of theillumination light beam IU on the wafer W is previously measured, and itis stored in the storage unit in the illumination control system 10. Theillumination control system 10 controls, for example, the laser powersource 17 and the dimming unit 18 so that the illuminance of theillumination light beam IU on the wafer W has a target value set by themain control system 13.

Next, the arrangement of the modified illumination mechanism 19 of thisembodiment is the same as that of the modified illumination mechanism ofthe first embodiment having been explained with reference to FIGS. 3 and4. It is possible to perform the ordinary illumination and the modifiedillumination (including the annular illumination) while the light amountloss is extremely minute. Further, it is possible to continuously andarbitrarily change the condition of the annular illumination (forexample, the outer diameter, the inner diameter, and the annular ratioof the secondary light source). Further, it is possible to switch the σvalue of the illumination optical system in a state in which the lightamount loss is substantially absent, by switching the magnification ofthe laser beam LB2 by the aid of the beam expander 42A, 42B.

The modified illumination mechanism 19A based on the diffracting opticalelement (DOE) system or the modified embodiment thereof may be used inplace of the modified illumination mechanism 19 of this embodiment, ashaving been explained with reference to FIG. 5. Accordingly, it ispossible to switch the ordinary illumination and the modifiedillumination without causing any substantial loss of the light amount ofthe incoming laser beam LB. In this arrangement, the light-outgoingplane 49 shown in FIG. 5 corresponds to the arrangement plane of thediaphragm-switching member 27 shown in FIG. 11.

With reference to FIG. 11 again, a laser beam LB1, which has passedthrough the modified illumination mechanism 19, comes into the bent typerod-shaped optical member 56 via the diaphragm-switching member 27, thelight-collecting lens 21, and the mirror 55. Explanation will be made indetail below for the arrangement and the function of the bent typerod-shaped optical member 56. At first, a reflective film of a metalfilm such as chromium or a multilayered reflective film may be formedbeforehand on the outer surfaces (reflecting surfaces) of the rodmembers 57A to 57G and the mirror members 58A to 58F which constitutethe bent type rod-shaped optical member 56. Other than the above, thetotal reflection may be utilized, for example, for the side surfaces ofthe prism-shaped rod members 57A to 57G and the reflecting surfaces ofthe mirror members 58A to 58F.

It is necessary that the optical members, which constitute the rodmembers 57A to 57G and the mirror members 58A to 58G, have goodtransmittance with respect to the laser beam LB2 (exposure light beam).Such an optical member is exemplified as follows. That is, when thelaser beam LB2 is the KrF excimer laser (wavelength: 248 nm), it ispossible to use, for example, fused quartz glass or synthetic quartzglass. When the laser beam LB2 is the ArF excimer laser (wavelength: 193nm), it is possible to use, for example, synthetic quartz glass orfluorite (CaF₂). When the laser beam LB2 is the F₂ laser (wavelength:157 nm), it is possible to use, for example, synthetic quartz glassdoped with an impurity such as fluorine and fluorite or magnesiumfluoride (MgF₂). When the laser beam LB2 has a wavelength of not morethan about 150 nm, for example, as in the case of the Kr₂ laser(wavelength: 146 nm), it is possible to use, for example, fluorite ormagnesium fluoride. Even when the material having a high transmittanceas described above is used for the bent type rod-shaped optical member56, it is feared that the heat is generated when the laser beam LB2repeatedly passes through the inside of the material. Accordingly, it isdesirable that a cooling mechanism for circulating a cooling medium, aheat-absorbing mechanism such as a Peltier element, or aheat-discharging mechanism such as a heat pipe is provided to verticallyinterpose the bent type rod-shaped optical member 56 thereby so that thetemperature of the bent type rod-shaped optical member 56 is controlled.Accordingly, it is possible to avoid the heat generation of the benttype rod-shaped optical member 56.

On the other hand, FIG. 12(a) shows a rod member 57X having a length LXwith an oblong cross-sectional configuration in which the width of oneside is d. FIG. 12(b) shows a rod member 57Y having a length LY (LY isfairly longer than LX) with an oblong cross-sectional configuration inwhich the width of one side is d. The former rod member 57X correspondsto the conventional rod integrator. It is assumed that the laser beamLB2 having an angular aperture θR (aperture half angle) comes from alight-collecting point 75 respectively into substantially entiresurfaces of the light-incoming planes of the rod members 57X, 57Y.Further, it is assumed that the length LX is shorter than d/tanθR, andthe length LY is longer than d/tanθR and shorter than 2·d/tanθR asfollows.

0<LX<d/tanθR  (11A)

d/tanθR<LY<2·d/tanθR  (11B)

In this case, as shown in FIG. 12(a), two light source images (secondarylight sources) 77A, 78A are formed as virtual images over and under thelight-collecting point 75 in accordance with the reflection effected bythe rod member 57X. The light-outgoing plane 76X of the rod member 57X,i.e., the plane conjugate with the reticle is illuminated in asuperimposed manner with laser beams coming from the three light sourceimages. On the other hand, as shown in FIG. 12(b), four light sourceimages 77A, 77B, 78A, 78B are formed as virtual images over and underthe light-collecting point 76 in accordance with the reflection effectedby the rod member 57Y. The light-outgoing plane 76Y of the rod member57Y is illuminated in a superimposed manner with laser beams coming fromthe five light source images. As a result, if the length LY of the rodmember 57Y is set as follows with an integer m of not less than 2, thelight-outgoing plane 76Y is illuminated in a superimposed manner with(2·m+1) individuals of light source images. It is appreciated that thenumber of individuals of superimposed light source images is increasedas the length LY is lengthened, and thus the uniformity of theilluminance distribution is improved owing to the integration effect.

(m−1)d/tanθR<LY<m·d/tanθR  (12)

The formation of the (2·m+1) individuals of light source images can bealso regarded to be equivalent to the fact that the number of wave frontdivision is (2·m+1). The sum of the lengths of the rod members 57A to57G of the bent type rod-shaped optical member 56 of this embodimentshown in FIG. 11 corresponds to one obtained in a case in which thelength LY of the rod member 57Y shown in FIG. 12(b) is allowed to havesuch a length that the value of the integer m in the expression (12) isset, for example, to be about 10 to 50, and the number of wave frontdivision is set to be about 20 to 100. However, the reticle in thisembodiment is illuminated with the oblong illumination area. Therefore,as shown in FIG. 12(c), the cross-sectional configuration of the rodmember 57Y is an oblong configuration in which the length in thedirection (Y direction) corresponding to the scanning direction SD is d,and the length dX in the direction (non-scanning direction: X direction)perpendicular to the scanning direction is, for example, several timesthe length d. This relationship also holds for the rod members 57A to57G shown in FIG. 11 in the same manner as described above. As a result,the number of wave front division in the non-scanning direction islowered to a fraction of that in the scanning direction. In order toavoid such a situation, for example, the angular aperture of theincoming laser beam LB2 in the non-scanning direction may be increasedaccording to the expression (2).

As described above, if the number of wave front division is merelyincreased, then the length of the rod member is long, and theillumination optical system is large-sized. Accordingly, the bent typerod-shaped optical member 56 shown in FIG. 11 adopts the arrangement inwhich one long rod member is bent by 90° at six positions respectively.As a result, the illumination optical system of this embodiment can beminiaturized. Further, it is possible to increase the number of wavefront division, and it is possible to improve the uniformity of theilluminance distribution when the reticle R is illuminated.

Further, the widths d1 to d7 in the bending directions of the rodmembers 57A to 57G of the bent type rod-shaped optical member 56 shownin FIG. 11 are set to be gradually widened from the light-incoming sideto the light-outgoing side as follows.

d 1<d 2<d 3<d 4<d 5<d 6<d 7  (13)

The reason of this arrangement will be explained. At first, as shown inFIG. 13(a), if it is assumed that a rod member 57Z having the same widthd1 is arranged for the first stage rod member 57A having the width d1with a mirror 58Z intervening therebetween, hatched portions EA, EB ofthe laser beam LB2 coming into the rod member 57A fail to arrive at therod member 57Z due to the shading or eclipse in some cases. In othercases, the hatched portions EA, EB are transmitted to the outside whenthe total reflection is utilized, because the angle of incidence intothe side surface is small. As a result, the light amount loss isincreased. On the contrary, as shown in FIG. 13(b), when the rod member57B having the width d2 (>d1) is arranged for the first stage rod member57A with a large mirror 58A′ intervening therebetween, most of the laserbeam LB2 coming into the rod member 57A is transmitted to the rod member57B as it is. Therefore, an advantage is obtained such that the lightamount loss is decreased. Further, in the case of the bent typerod-shaped optical member 56 shown in FIG. 11, the prism type mirrormember 58A, which is adjusted to the size of the next stage rod member57B, is used in place of the mirror 58A′ shown in FIG. 13(b). Therefore,the adjoining rod members 57A, 57B can be stably fixed, and the lightamount loss is further decreased. The other mirror members 58B to 58Fare also arranged in this way in the same manner as described above. Inthis arrangement, for example, the mirror member 58A and the rod member57B may be integrated into one unit, and the following mirror membersand the rod members may be also successively integrated into one unit inthe same manner as described above. Accordingly, it is easy to assembleand adjust the bent type rod-shaped optical member 56.

The number of individuals of the rod members 57A to 57G for constructingthe bent type rod-shaped optical member 56 is arbitrary provided thatthe number of individuals is not less than two. Alternatively, the benttype rod-shaped optical member 56 may be constructed by combining aplurality of mirrors so that the optical path of the laser beam iscovered therewith, without using any refracting member. In this case, ahigh transmittance is obtained by purging the interior with a so-calledinert gas having a high transmittance with respect to the laser beam inthe ultraviolet region such as nitrogen gas or rare gas (for example,helium gas), or by allowing the interior to be in vacuum. Thisarrangement is especially effective when the laser beam has a shortwavelength as in the Ar₂ laser (wavelength: 126 nm). When the wavelength(exposure wavelength) of the laser beam is not less than about 200 nm,for example, the interior may be purged with dry air. When the interioris allowed to be in vacuum, the extreme ultraviolet light beam (EUVlight beam) such as soft X-ray can be also used as the exposure lightbeam.

Next, explanation will be made for an example of the operation forcontrolling the exposure amount of the projection exposure apparatus ofthis embodiment. With reference to FIG. 10, in this embodiment, theuneven illuminance sensor 2 is moved to the front side in the scanningdirection (Y direction) with respect to the slit-shaped exposure area ofthe projection optical system 3 in a state in which a see-through testreticle formed with no transfer pattern is arranged beforehand in placeof the reticle R before the exposure. Test light emission is performedby the exposure light source 9, and the light-receiving section 2 a ofthe uneven illuminance sensor 2 is moved at a predetermined pitch totraverse the exposure area in the scanning direction as shown in FIG.16(b). During this process, for example, the uneven illuminance sensor 2receives the illumination light beam IU of several tens pulses everytime when the uneven illuminance sensor 2 is moved at the predeterminedpitch to supply a photoelectrically converted signal to the main controlsystem 13. The main control system 13 allots an average value of thephotoelectrically converted signals as the illuminance Pi (i=1, 2, 3, .. . ) for a series of measuring points at the predetermined pitch.

A curve 60A shown in FIG. 16(a) illustrates an example of theilluminance distribution in the scanning direction of the exposure areaobtained as described above. In FIG. 16(a), the curve 60A is actually anaggregate of digital data of the predetermined pitch. After that, themain control system 13 effects Fourier transformation (for example, FFT)for the curve 60A to determine a pitch Q1 in the scanning direction (Ydirection) of the spatial frequency component having the largestamplitude. The pitch Q1 is stored in the storage unit 13 a. In thisembodiment, the uniformity of the illuminance distribution isconsiderably improved on the reticle R and the wafer W, owing to the useof the bent type rod-shaped optical member 56 and the modifiedillumination mechanism 19 shown in FIG. 11. Therefore, the pitch Q1 canbe also regarded as the pitch of the remaining interference fringes(speckles). That is, assuming that the slit-shaped exposure area on thewafer W shown in FIG. 10 is the exposure area 59 having the width (slitwidth) D in the scanning direction SD (Y direction) as shown in FIG.15(a), the illuminance distribution in the scanning direction of theillumination light beam (exposure light beam) on the exposure area 59 isperiodically fluctuated at the pitch Q in average as shown by a curve 60in FIG. 15(b), even when the transmittance distribution of the reticleis uniform. It is assumed that the pulse light emission of theillumination light beam IU is performed every time when the wafer W ismoved by an integral multiple n·Q1 (n=1 in FIG. 15(a)) of the pitch Q1in the Y direction as indicated by light emission positions 71A, . . . ,71B, . . . in FIG. 15(b) during the scanning exposure in this state. Onthis assumption, the totalized exposure amount on the wafer W isgradually changed to a periodic distribution having intense contrast asindicated by exposure amount distribution curves 72A, 72B, . . . , 72Ein FIG. 15(c). As a result, the unevenness of the exposure amount isgenerated.

Accordingly, in this embodiment, the distance Q2, by which the wafer Wis moved in the Y direction every time when the pulse light emission ofthe illumination light beam IU is performed, is set to be in arelationship of non-integral multiple as indicated by light emissionpositions 73A, . . . , 73B, . . . with respect to the pitch Q1 of theilluminance distribution represented by a curve 60 during the scanningexposure as shown in FIG. 15(d). This means the fact that n·Q1 is notcoincident with Q2 even when an arbitrary integer n is used as in thefollowing expression.

Q 2≠n·Q 1  (14)

As a result, the totalized exposure amount on the wafer W is graduallychanged to a flat distribution as indicated by exposure amountdistribution curves 74A, 74B, . . . , 74E in FIG. 15(e). The unevennessof the illuminance distribution of the illumination light beam IU itselfis not converted into the unevenness of the totalized exposure amount.Therefore, it is possible to improve the uniformity of the totalizedexposure amount distribution in each of the shot areas on the wafer Wafter the scanning exposure.

In order to specifically explain the method for setting respectiveparameters during the scanning exposure, it is assumed that E [j/mm²]represents the resist sensitivity (proper exposure amount) on the waferW shown in FIG. 10, and p [j/mm²] represents the average pulse energy onthe wafer W. On this assumption, it is necessary that the followingrelationship holds within a predetermined allowable range by using thenumber of exposure pulses N (≧N_(min)).

E=N·P  (15)

It is assumed that D [mm] represents the slit width of the exposure areaon the wafer W, V [mm/s] represents the scanning velocity of the waferstage 1, V_(max) represents the upper limit of the scanning velocity V,f [/s] represents the oscillation frequency of the laser beam LB at theexposure light source 9, and f_(max) represents the upper limit of theoscillation frequency f. On this assumption, the distance Q2 [mm] bywhich the wafer W is moved every time when the pulse light emission isperformed as shown in FIG. 15(d), and the number of exposure pulses Nare represented by the following expressions.

Q 2=V/f≠n·Q 1  (16)

N=f·(D/V)≧N _(min)  (17)

If the expression (15) is substituted with the expression (17), thefollowing expression is obtained.

E·V=f·P·D  (18)

Assuming that the slit width D is fixed, the main control system 13 setsthe scanning velocity V to the upper limit value V_(max) in order toenhance the throughput, and it calculates the oscillation frequency f inaccordance with the expression (18) as follows.

V=V _(max) , f=E·V/(P·D)  (19)

The main control system 13 compares the resultant oscillation frequencyf with the upper limit value f_(max). Further, the main control system13 compares the distance Q2 (=V/f) in the expression (16) with the pitchQ1 stored in the storage unit 13 a. If the oscillation frequency fexceeds the upper limit value f_(max), or if Q2 in the expression (16)equals to n·Q1 within a predetermined allowable range, then the maincontrol system 13 sets the scanning velocity V, for example, to a valuewhich is smaller than the upper limit value V_(max) by predetermined ΔVto calculate the oscillation frequency f again from the secondexpression of the expression (19). The oscillation frequency f iscalculated again by gradually decreasing the scanning velocity V by ΔVuntil the oscillation frequency f obtained as described above is notmore than the upper limit value f_(max), and Q2≠n·Q1 in the expression(16) holds while exceeding the predetermined allowable range.Accordingly, the expression (16) finally holds, and the values of theoscillation frequency f and the scanning velocity V are determined asvalues within the upper limit values. The oscillation frequency f is setin the illumination control system 10.

Corresponding thereto, the illumination control system 10 sets theoscillation frequency f of the laser beam LB for the laser power source17 shown in FIG. 11. The main control system 13 sets the scanningvelocity V of the wafer W (scanning velocity of the reticle is V/β) forthe wafer stage control system 11 and the reticle stage control system12 to start the scanning exposure. Accordingly, the respective shotareas on the wafer W are exposed by transfer with the image of thepattern on the reticle R respectively. During the scanning exposure, thetotalized exposure amount for each of the shot areas on the wafer W isindirectly measured by the aid of an unillustrated integrator sensor.The output of the pulse light from the exposure light source 9 is finelyadjusted on the basis of the measured value.

As described above, in this embodiment, the bent type rod-shaped opticalmember 56 is arranged in the illumination system 8. Therefore, even whenthe coherence (spatial coherence) of the laser beam LB2 as the exposurelight beam is high, the uniformity of the illuminance distribution isimproved in the illumination area on the reticle R and consequently onthe exposure area on the wafer W. Further, even when the interferencefringes (for example, speckles) remain in the illumination area, theunevenness of the totalized exposure amount after the scanning exposureis extremely decreased by satisfying the condition represented by theexpression (16). It is possible to obtain high line width uniformity.Further, the influence of interference fringes can be reduced.Accordingly, it is possible to decrease the number of pulse lightemission necessary to perform the exposure once. It is also possible toexpect the improvement in throughput brought about by the reduction ofthe exposure time.

Further, it is possible to realize, for example, the ordinaryillumination, the annular illumination, and the small a valueillumination with the small space while the light amount loss scarcelyoccurs. Therefore, it is also possible to improve the throughput for thelayer in which the resist sensitivity is low. On the other hand, when itis enough to use the same degree of exposure time as that of theexemplary conventional technique, the upper limit (rating) of the outputof the exposure light source 9 can be set to be low. Accordingly, it isalso possible to realize the decrease in cost of the projection exposureapparatus and the long service life of the exposure light source 9itself.

Next, explanation will be made with reference to FIG. 14 for otherillustrative arrangements of the bent type rod-shaped optical member 56of the embodiment described above.

An illustrative arrangement shown in FIG. 14(a) comprises four mirrormembers and three rod members. A mirror member 58G for bending theoptical path by 90° in shaped (like a shape of staple) configuration, arod member 57H, a mirror member 58H, a rod member 57I, a mirror member58I, a rod member 57J, and a mirror member 58J are arranged in thisorder from the light-incoming side of the laser beam LB2.

An illustrative arrangement shown in FIG. 14(b) also comprises fourmirror members and three rod members. A mirror member 58G, a rod member57H, a mirror member 58K for bending the optical path by 180°, a rodmember 57K, a mirror member 58L for bending the optical path by 180°, arod member 57L, and a mirror member 58M are arranged in a substantially“S-shaped” configuration in this order from the light-incoming side ofthe laser beam LB2.

In an illustrative arrangement shown in FIG. 14(c), the laser beam LB2(linearly polarized light beam in this case) is introduced into aloop-shaped optical path by the aid of a polarizing beam splitter 58N.The laser beam LB2, which has passed through the loop-shaped opticalpath, is extracted by the aid of a polarizing beam splitter 85N.Actually, the polarizing beam splitter 58N is arranged in a state ofbeing rotated by 90° about the optical axis. In this case, the laserbeam LB2 is radiated and extracted in the direction perpendicular to theplane of paper of FIG. 14(c), without being affected by the loop-shapedoptical path. The loop-shaped optical path comprises a rod member 57M, amirror member 580 for bending the optical path by substantially 60°, arod member 57N, a mirror member 58P for bending the optical path bysubstantially 120°, a rod member 570, a mirror member 58Q, and a rodmember 57P which are arranged in this order from the light-incomingside.

Also in the respective illustrative embodiments shown in FIG. 14, it ispossible to decrease the light amount loss by gradually widening thewidths of the series of rod members in the bending direction. When thebent type rod-shaped optical member 56 is constructed by bending andarranging three or more rod members (by bending the optical member 56 atthree or more positions) as in the respective illustrative embodimentsshown in FIG. 14, it is possible to especially miniaturize theillumination optical system on condition that the necessary uniformityof the illuminance distribution is obtained.

As described above, in this embodiment, the exposure method based on theuse of the KrF excimer laser has been explained. However, the bent typerod-shaped optical member 56 will be also effective when the laser beamhaving coherence and having a shorter wavelength will be used as theexposure light beam in future, including, for example, the ArF excimerlaser (193 nm), the F₂ laser (157 nm), the Ar₂ laser beam (wavelength:126 nm), the high harmonic wave of the YAG laser, and the high harmonicwave of the semiconductor laser. However, when the laser beam in thevacuum ultraviolet region is used as described above, it is feared thatthe bent type rod-shaped optical member 56 is damaged due to anyconcentration of energy, or any cloudy substance, which is formed by thechemical reaction between the laser beam and any minute organicsubstance or the like with which the atmosphere is contaminated, adheresto the light-incoming/outgoing plane of the bent type rod-shaped opticalmember 56.

Accordingly, the rod member 57A on the light-incoming side and the rodmember 57G on the light-outgoing side of the bent type rod-shapedoptical member 56 shown in FIG. 11 may be exchangeable. Alternatively, atransparent cover may be provided so that the light-incoming/outgoingplane is covered therewith in order to avoid any adhesion of the cloudysubstance. The interior of the cover may be purged with a gas (forexample, an inert gas as described above) which is clear and which has ahigh transmittance with respect to the laser beam. In order to avoid anygeneration of organic matter or the like, it is desirable that theplurality of optical members (for example, rod members) for constructingthe bent type rod-shaped optical member 56 are held in an integratedmanner with a holding tool the like, without using the adhesive or thefiller. Further, the generation of organic matter or the like can beavoided by coating, for example, the inside of the cover, for example,with Teflon.

In the illustrative arrangement shown in FIG. 11, thediaphragm-switching member 27, which serves as the aperture diaphragm (adiaphragm) of the illumination system, is arranged on the light-outgoingplane of the modified illumination mechanism 19. However, thediaphragm-switching member 27 may be arranged, for example, on the pupilplane (Fourier transformation plane with respect to the pattern plane ofthe reticle R) between the relay lens system 31 and the condenser lenssystem 7.

In order to further reduce the interference fringes, in the illustrativearrangement shown in FIG. 11, for example, the mirror 55 may be vibratedto slightly periodically vary the angle of incidence of the laser beamLB2 coming into the bent type rod-shaped optical member 56.

Further, the direction, in which the coherence of the laser beam LB2 ishigh, may be allowed to make intersection with the non-scanningdirection which is perpendicular to the scanning direction for thereticle R. For example, the direction, in which the coherence is high,may be made substantially coincident with the scanning direction. Bydoing so, the influence of the speckle may be reduced by means of theaveraging effect brought about by the scanning exposure. In thisarrangement, as for the non-scanning direction, if necessary, the mirror55 may be vibrated (or a vibrating mirror may be used) as describedabove in relation to the non-scanning direction to uniformize the unevenilluminance (uneven exposure amount). Besides this method, thedirection, in which the coherence of the laser beam LB2 is high, may bemade coincident with the non-scanning direction to uniformize the unevenilluminance (uneven exposure amount) in relation to the non-scanningdirection by using an illuminance-uniformizing means such as thevibrating mirror or a dispersing plate or the like.

Next, the exposure apparatus according to the first embodiment can beproduced such that the projection optical system and the illuminationoptical system constructed by the optical members such as the delayoptical system 22 shown in FIG. 2 are assembled to a main exposureapparatus body to perform optical adjustment, the reticle stage and thewafer stage composed of a large number of mechanical parts are attachedto the main exposure apparatus body to connect wirings and pipings, andoverall adjustment (for example, electric adjustment and confirmation ofoperation) is performed. It is desirable that the exposure apparatus isproduced in a clean room in which, for example, the temperature and thecleanness are managed. The exposure apparatus according to the secondembodiment can be produced in the same manner as described above.

A semiconductor device is produced, for example, by performing a step ofdesigning the function and the performance of the device, a step ofproducing a reticle based on the foregoing step, a step of producing awafer from a silicon material, a step of exposing a wafer with a patternon a reticle by using each of the projection exposure apparatuses of theembodiments described above, a step of assembling the device (includinga dicing step, a bonding step, and a packaging step), and an inspectionstep.

In the embodiments described above, the present invention is applied tothe scanning exposure type projection exposure apparatus based on theuse of the pulse light beam. However, it is clear that the presentinvention is also applicable to a scanning exposure type projectionexposure apparatus which uses a continuous light beam as an exposurelight beam, and a full field exposure type projection exposure apparatussuch as a stepper which uses a continuous light beam or a pulse lightbeam, and the present invention is also applicable to an illuminationoptical system, for example, for an exposure apparatus of the proximitysystem in which no projection optical system is used. Further, anillumination optical system is constructed by only a reflecting opticalelement in some cases depending on the wavelength of the exposure lightbeam. However, the present invention is also applicable to such anillumination optical system.

Further, the exposure apparatus of the present invention is not limitedto the exposure apparatus for producing semiconductors, which is alsowidely applicable, for example, to an exposure apparatus for producing aliquid crystal in which an angular type glass plate is exposed with aliquid crystal display element pattern, an exposure apparatus forproducing a plasma display element, an exposure apparatus for producing,for example, a micromachine, a thin film magnetic head, and an imagepickup element (CCD or the like), and an exposure apparatus forproducing a mask itself on which a device pattern is drawn in accordancewith the transfer system.

In place of the excimer laser or the like, it is also preferable to use,as an exposure light beam, a high harmonic wave which is obtained suchthat a single wavelength laser in the infrared region or the visibleregion, which is oscillated from a DFB (Distributed feedback)semiconductor laser or a fiber laser, is amplified with a fiberamplifier doped with, for example, erbium (Er) (or both of erbium andytterbium (Yb)), followed by performing wavelength conversion into anultraviolet light beam by using a nonlinear optical crystal. Forexample, assuming that the oscillation wavelength of the singlewavelength laser is within a range of 1.544 to 1.553 μm, an 8-fold highharmonic wave within a range of 193 to 194 nm, i.e., an ultravioletlight beam having approximately the same wavelength as that of the ArFexcimer laser is obtained. Assuming that the oscillation wavelength iswithin a range of 1.57 to 1.58 μm, a 10-fold high harmonic wave within arange of 157 to 158 nm, i.e., an ultraviolet light beam havingapproximately the same wavelength as that of the F₂ laser is obtained.

Accordingly, the present invention is not limited to the embodimentsdescribed above, which may be embodied in other various forms within arange without deviating from the gist or essential characteristics ofthe present invention. All of the contents of disclosure of JapanesePatent Application No. 11-137840 filed on May 18, 1999, Japanese PatentApplication No. 11-324748 filed on Nov. 15, 1999, and Japanese PatentApplication No. 11-358204 filed on Dec. 16, 1999 includingspecifications, claims, drawings, and abstracts are quoted as they areand incorporated into this application.

INDUSTRIAL APPLICABILITY

According to the first exposure method and the first illuminatingapparatus of the present invention, the light fluxes are allowed to passthrough the substantially closed loop-shaped optical path, and theplurality of light fluxes, which have passed through the loop-shapedoptical path a variety of numbers of times depending on the angularapertures respectively, are superimposed. Accordingly, the temporalcoherence of the light flux is greatly lowered. Therefore, even when theillumination light beam (exposure light beam) having high coherence isused, it is possible to obtain a substantially uniform illuminancedistribution on a pattern of a transfer objective, without complicatingand large-sizing the illumination optical system so much and withoutprolonging the illumination time (exposure time).

According to the first and second exposure apparatuses of the presentinvention, the unevenness of the exposure amount scarcely occurs evenwhen the illuminance of the exposure light beam is increased. Therefore,it is possible to mass-produce a device having a high function with ahigh throughput.

Even when the illumination system is switched into the ordinaryillumination, the illumination with the small σ value, or the modifiedillumination (annular illumination) in a state in which the light amountloss of the exposure light beam is decreased, the interference fringesare scarcely generated. Therefore, it is possible to perform theexposure at a high throughput even for a layer having low resistsensitivity. Further, when it is enough that the illuminance is at thesame degree as that used in the conventional technique, it is possibleto set the low output specification for the laser light source as theexposure light source. Therefore, it is possible to realize the low costand the long service life of the laser light source.

On the other hand, according to the second exposure method of thepresent invention, the optical path for the exposure light beam(illumination light beam) is bent. Therefore, even when the exposurelight beam having high coherence is used, it is possible to improve theuniformity of the illuminance distribution on a pattern of a transferobjective without large-sizing the illumination optical system so muchand without prolonging the illumination time (exposure time).

According to the third exposure method of the present invention, whenthe scanning exposure is performed with the pulse light beam, the timingfor the pulse light emission is controlled to be in a predeterminedstate. Therefore, even when the exposure light beam having highcoherence is used, it is possible to improve the uniformity of thetotalized exposure amount distribution after the exposure withoutlarge-sizing the illumination optical system so much and withoutprolonging the illumination time (exposure time).

According to the second illuminating apparatus, the third and fourthexposure apparatus, and the fifth exposure apparatus of the presentinvention, it is possible to carry out the corresponding exposuremethods of the present invention respectively. Further, the unevennessof the exposure amount is decreased, even when the illuminance of theexposure light beam (illumination light beam) is increased. Therefore,it is possible to mass-produce a device having a high function at a highthroughput. Further, when it is enough that the illuminance is at thesame degree as that used in the conventional technique, it is possibleto set the low output specification for the laser light source as theexposure light source. Therefore, it is possible to realize the low costand the long service life of the laser light source.

What is claimed is:
 1. An exposure method for illuminating a firstobject with an exposure light beam to transfer a pattern on the firstobject onto a second object, the exposure method comprising: adjustingthe exposure light beam into light fluxes having a predetermined angularaperture distribution, and allowing the adjusted light fluxes to passthrough a substantially closed loop-shaped optical path so that aplurality of light fluxes, which have passed through the loop-shapedoptical path a variety of numbers of times depending on angularapertures respectively, are superimposed and guided to the first object.2. A method for producing a device, comprising the step of transferringa device pattern onto an object by using the exposure method as definedin claim
 1. 3. The exposure method according to claim 1, wherein theadjusted light fluxes are collected so that a light-collecting point ofthe adjusted light fluxes is positioned on a plane which is differentfrom a light-incoming plane of an optical member which defines theloop-shaped optical path.
 4. The exposure method according to claim 3,wherein the plurality of light fluxes are radiated from the opticalmember through a window which is smaller than a cross-sectional area ofthe transmitting section of the optical member in which the adjustedlight fluxes are internally reflected.
 5. An illuminating apparatus forilluminating a pattern on an illumination objective with an illuminationlight beam from a light source, the illuminating apparatus comprising:an optical member including a window which receives the illuminationlight beam from the light source, wherein a plurality of light fluxes,which are obtained by allowing light fluxes incoming from the window topass through the optical member a variety of numbers of times dependingon angular apertures respectively, are superimposed and radiated towardthe illumination objective.
 6. The illuminating apparatus according toclaim 5, wherein: an angular aperture-adjusting optical system whichadjusts the illumination light beam from the light source into lightfluxes having a predetermined angular aperture distribution is arrangedbetween the light source and the optical member; and a multiple lightsource-forming optical system which forms a plurality of light sourceimages from the illumination light beam from the optical member, and acondenser optical system which radiates light fluxes from the pluralityof light source images onto the illumination objective in a superimposedmanner are arranged between the optical member and the illuminationobjective.
 7. The illuminating apparatus according to claim 5, whereinthe window is arranged at a position which is eccentric from a centralaxis of the optical member.
 8. The illuminating apparatus according toclaim 5, wherein the optical member includes one or a plurality of outersurface reflection type member or members arranged in a ring-shapedconfiguration, the outer surface reflection type member having an outercircumferential surface which serves as a reflecting surface forallowing the illumination light beam to pass through an interiorthereof.
 9. The illuminating apparatus according to claim 5, wherein theoptical member includes a plurality of prism-shaped transmitting memberssuccessively arranged in a ring-shaped configuration together withintervening reflecting surfaces, the transmitting members havingrespective outer circumferential surfaces which serve as reflectingsurfaces for allowing the illumination light beam to pass through aninterior thereof.
 10. The illuminating apparatus according to claim 9,wherein: the window of the optical member is an aperture which is formedat a part of the reflecting surface at a boundary of the transmittingmember; and the illumination light beam, which has passed through theoptical member, is radiated through the aperture.
 11. The illuminatingapparatus according to claim 9, wherein: the window of the opticalmember is one surface of a prism member formed at a part of thereflecting surface at a boundary of the transmitting member; and theillumination light beam, which has passed through the optical member, isradiated through another surface of the prism member.
 12. Theilluminating apparatus according to claim 9, wherein the window of theoptical member is a reflecting section which is formed at the inside ofthe transmitting member.
 13. An exposure apparatus which transfers apattern on a first object onto a second object, wherein the pattern onthe first object is illuminated with an illumination light beam from theilluminating apparatus as defined in claim
 5. 14. The exposure apparatusaccording to claim 13, wherein the illuminating apparatus includes anoptical unit which branches the illumination light beam from the lightsource into a plurality of individuals to generate a plurality of lightfluxes having mutually different intensity distributions and whichcombines the plurality of light fluxes to effect radiation, the opticalunit being arranged between the light source and the optical member inorder to change an illumination condition for the first object.
 15. Theexposure apparatus according to claim 13, wherein the illuminatingapparatus comprises a light-collecting optical element which collectsthe illumination light beam incoming to the optical member so that alight-collecting point of the illumination light beam is positioned on aplane which is different from a light-incoming plane of the opticalmember.
 16. The exposure apparatus according to claim 15, wherein theoptical member has a window which is smaller than a cross-sectional areaof the transmitting section in which the light fluxes incoming from thewindow are internally reflected, and the plurality of light fluxes areradiated from the optical member through the window.
 17. An exposureapparatus provided with an illumination system which illuminates a firstobject with an exposure light beam in which a second object is exposedwith the exposure light beam via the first object, the exposureapparatus comprising: an optical member which includes a transmittingsection which internally reflects the exposure light beam in theillumination system and changes a traveling direction thereof, wherein:the optical member is formed with an aperture which is smaller than across-sectional area of the transmitting section in order to radiate theexposure light beam.
 18. The exposure apparatus according to claim 17,wherein the illumination system includes an optical unit which isarranged between a light source which generates the exposure light beamand the optical member in order to change an illumination condition forthe first object.
 19. The exposure apparatus according to claim 18,wherein the optical unit branches the exposure light beam into aplurality of individuals to generate a plurality of beams havingmutually different intensity distributions, and the optical unitcombines the beams to effect radiation.
 20. The exposure apparatusaccording to claim 18, wherein the optical unit exchanges a diffractingoptical element which introduces the exposure light beam thereinto togenerate a diffracted beam, with another diffracting optical element.21. The exposure apparatus according to claim 17, wherein the opticalmember converts the exposure light beam into a plurality of light fluxeswhich pass through different apertures of the transmitting section,respectively.
 22. The exposure apparatus according to claim 21, whereinthe illumination system comprises a light-collecting optical elementwhich collects the exposure light beam so that a light-collecting pointof the exposure light beam is positioned on a plane which is differentfrom a light-incoming plane of the optical member.
 23. An exposuremethod for illuminating a first object with an exposure light beam toexpose a second object with the exposure light beam having passedthrough a pattern on the first object, the exposure method comprising:introducing the exposure light beam into a plane which is substantiallyconjugate with a pattern plane of the first object via an openlight-feeding optical path which is surrounded by reflecting surfacesand which has at least one bent section, and introducing, into the firstobject, the exposure light beam having passed through the plane.
 24. Theexposure method according to claim 23, wherein a width of thelight-feeding optical path on a light-outgoing side is wider than awidth of the light-feeding optical path on a light-incoming side in abending direction brought about by the bent section.
 25. The exposuremethod according to claim 24, wherein the exposure light beam is pulseemitted, and the second object is scanning-exposed with the exposurelight beam having passed through the first object while synchronousmovement of the first object and the second object, and a distance ofmovement of the second object in the scanning direction during one cycleof pulse light emission of the exposure light beam is set to be anon-integral multiple of a repeating pitch of an intensity distributionof the exposure light beam on the second object in the scanningdirection.
 26. A method for producing a device, comprising a step oftransferring a device pattern onto an object by using the exposuremethod as defined in claim
 23. 27. An exposure method for illuminating afirst object with a pulse-emitted exposure light beam and synchronouslymoving the first object and a second object to perform scanning exposurefor the second object with the exposure light beam having passed througha pattern on the first object, the exposure method comprising:previously measuring a repeating pitch of an intensity distribution ofthe exposure light beam on the second object in a scanning direction forthe second object; and setting a distance of movement of the secondobject in the scanning direction during one cycle of pulse lightemission of the exposure light beam to be a non-integral multiple of themeasured pitch.
 28. The exposure method according to claim 27, whereinthe repeating pitch of the intensity distribution of the exposure lightbeam on the second object is a pitch of a spatial frequency componenthaving a largest amplitude in the intensity distribution.
 29. A methodfor producing a device, comprising a step of transferring a devicepattern onto an object by using the exposure method as defined in claim23.
 30. An illuminating apparatus which illuminates a pattern on anillumination objective with an illumination light beam from a lightsource, the illuminating apparatus comprising: a multiple lightsource-forming optical system which includes a plurality of transmittingsections surrounded by reflecting surfaces respectively for allowing theillumination light beam to pass through an interior thereof, and one ora plurality of reflecting section or sections which bends an opticalpath for the illumination light beam at a boundary between the pluralityof transmitting sections, in which the illumination light beam isincorporated at one transmitting section of the plurality oftransmitting sections, and the illumination light beam is radiated fromanother transmitting section onto a plane that is substantiallyconjugate with a pattern plane of the first object; and a condenseroptical system which collects, onto the pattern, the illumination lightbeam having passed through the substantially conjugate plane.
 31. Theilluminating apparatus according to claim 30, wherein an illuminancedistribution-switching optical system, which switches an illuminancedistribution of the illumination light beam from the light source into afirst distribution that is enlarged in an area including an optical axisand a second distribution that is enlarged in an area apart from theoptical axis, is arranged between the light source and the multiplelight source-forming optical system.
 32. An exposure apparatuscomprising an illumination apparatus as defined in claim 31, whichilluminates a first object as an illumination objective with anillumination light beam from the illuminatin apparatus, wherein: asecond object is exposed with the illumination light beam having passedthrough a pattern on the first object.
 33. An exposure apparatuscomprising an illuminating apparatus as defined in claim 30 whichilluminates a first object as an illumination objective with anillumination light beam from the illuminating apparatus, wherein: asecond object is exposed with the illumination light beam having passedthrough a pattern on the first object.
 34. The exposure apparatusaccording to claim 33, wherein the plurality of the transmittingsections comprises a first transmitting section and a secondtransmitting section into which the illumination light beam is incomefrom the first transmitting section and a width of which is larger thanthat of the first transmitting section.
 35. An exposure apparatus havingan illumination system which illuminates a first object with an exposurelight beam, for exposing a second object with the exposure light beamvia the first object, the exposure apparatus comprising: an opticalmember which includes a transmitting section which internally reflectsthe exposure light beam in the illumination system, wherein: thetransmitting section of the optical member is bent at least at oneposition, and a width of the transmitting section after being bent islarger than a width of the transmitting section before being bent. 36.The exposure apparatus according to claim 35, wherein the illuminationsystem includes an optical unit which is arranged between a light sourcewhich generates the exposure light beam and the optical member in orderto change an illumination condition for the first object.
 37. Anexposure apparatus which illuminates a first object with an exposurelight beam from a pulse light source and synchronously moving the firstobject and a second object by a stage system to perform scanningexposure for the second object with the exposure light beam havingpassed through a pattern on the first object, the exposure apparatuscomprising: a storage unit which stores a repeating pitch of anintensity distribution of the exposure light beam on the second objectin a scanning direction for the second object; and a control systemwhich controls a light emission frequency of the pulse light source anda scanning velocity of the second object effected by the stage systemdepending on the stored pitch.
 38. The exposure apparatus according toclaim 37, further comprising an optical member which has a transmittingsection which internally reflects the exposure light beam in anillumination system which illuminates the first object with the exposurelight beam, and wherein the transmitting section of the optical memberis bent at least at one position, and a width of the transmittingsection after being bent is larger than a width of the transmittingsection before being bent.